What a strange challenge! I followed the expenses structure and achieved a working camping app - but it failed the challenge.
After many attempts at restructuring, I finally solved it. Here's my code:
 

camping.cmp

<aura:component   controller="CampingListController">
<!-- the Apex server side controller -->
<aura:attribute name="items" type="Camping_Item__c[]"/>
<c:campingHeader />
                <c:campingList items="{!v.items}"/>       
</aura:component>
 

campingList.cmp

<aura:component  controller="CampingListController">
    <aura:attribute name="items" type="Camping_Item__c[]"/>
<aura:handler name="init" action="{!c.doInit}" value="{!this}"/>
  
        <aura:attribute name="newItem" type="Camping_Item__c"
                    default="{'sobjectType' : 'Camping_Item__c',
                               'Name':'',
                               'Quantity__c' : '',
                               'Price__c' : ''}"/>
   
       
  <!-- BOXED AREA -->
  <fieldset class="slds-box slds-theme--default slds-container--small">
 
    <legend id="newCampItemForm" class="slds-text-heading--small
      slds-p-vertical--medium">
      Add Camping Item
    </legend>
 
    <!-- CREATE NEW CAMPING ITEM FORM -->
    <form class="slds-form--stacked">
 
      <div class="slds-form-element slds-is-required">
          <div class="slds-form-element__control">
              <ui:inputText aura:id="campItemName" label="Camping Item Name"
                  class="slds-input"
                  labelClass="slds-form-element__label"
                  value="{!v.newItem.Name}"
                  required="true"/>
          </div>
     </div>
 
     <div class="slds-form-element slds-is-required">
          <div class="slds-form-element__control">
              <ui:inputNumber aura:id="quantity" label="Quantity"
                  class="slds-input"
                  labelClass="slds-form-element__label"
                  value="{!v.newItem.Quantity__c}"
                  required="true"/>
 
          </div>
      </div>
 
      <div class="slds-form-element">
          <div class="slds-form-element__control">
              <ui:inputCurrency aura:id="price" label="Price"
                  class="slds-input"
                  labelClass="slds-form-element__label"
                  value="{!v.newItem.Price__c}"/>
          </div>
      </div>
 
      <div class="slds-form-element">
          <ui:inputCheckbox aura:id="packed" label="Packed?"
              class="slds-checkbox"
              labelClass="slds-form-element__label"
              value="{!v.newItem.Packed__c}"/>
      </div>
 
      <div class="slds-form-element">
          <ui:button label="Create Camping Item"
              class="slds-button slds-button--brand"
              press="{!c.clickCreateItem}"/>
      </div>
 
    </form>
    <!-- / CREATE NEW CAMPING ITEM FORM -->
 
  </fieldset>
    <!-- / BOXED AREA -->
   
   
   
 
   <div class ="slds-card slds-p-top--medium">
        <header class ="slds-card__header">
            <h3 class = "slds-text-heading--small">Items</h3>
        </header>
 
        <section class ="slds-card__body">
               <div id="list" class = "row">
               <aura:iteration items="{!v.items}" var="item">
                    <c:campingListItem item="{!item}"/>
                </aura:iteration>
            </div>
        </section>
 
    </div>
 
</aura:component>
 

campingListController.js

({
              
    // Load camping items from Salesforce
    doInit: function(component, event, helper) {
   
        console.log("call c.getItems: ");
        // Create the action
        var action = component.get("c.getItems");
        console.log("back from c.getItems: ");
   
        // Add callback behavior for when response is received
        action.setCallback(this, function(response) {
            var state = response.getState();
            if (component.isValid() && state === "SUCCESS") {
                component.set("v.items", response.getReturnValue());
            }
            else {
                console.log("Failed with state: " + state);
            }
        });
   
        // Send action off to be executed
        $A.enqueueAction(action);
    }, //doInit
   
   
    clickCreateItem: function(component, event, helper) {
       
        if(helper.validateCampingItem(component)){
            // Create the new camping item
            var newCampingItem = component.get("v.newItem");
            console.log(newCampingItem);
            helper.createItem(component, newCampingItem);
        }
 
 
    }, //clickCreateItem
   
})
 

campingListHelper.js

({
              
   createItem: function(component, campItem) {
       
        var action = component.get("c.saveItem");
        console.log('create');
        console.log('campitem='+campItem);
        action.setParams({ "campItem": campItem });
        console.log('back from set params');
        action.setCallback(this, function(response){
            var state = response.getState();
            if (component.isValid() && state === "SUCCESS") {
                var items = component.get("v.items");
                items.push(response.getReturnValue());
                component.set("v.items", items);
            }
        });
        $A.enqueueAction(action);
       
    },//createItem
   
 
    validateCampingItem: function(component, item) {
       
         // Simplistic error checking
        var validItem = true;
        console.log("validate item");
 
 
          // Name must not be blank
        var nameField = component.find("campItemName");
        var itemname = nameField.get("v.value");
        console.log("itemname="+itemname);
        if ($A.util.isEmpty(itemname)){
            validItem = false;
            nameField.set("v.errors", [{message:"Item name can't be blank."}]);
        }
        else {
            console.log("good name "+itemname);
            nameField.set("v.errors", null);
        }
 
 
                              // Price must not be blank
        var priceField = component.find("price");
        var itemprice = priceField.get("v.value");
        console.log("itemprice="+itemprice);
       
        if (isNaN(itemprice)){
            validItem = false;
            priceField.set("v.errors", [{message:"Item price can't be null."}]);
        }
        else {
            priceField.set("v.errors", null);
        }
        if ($A.util.isEmpty(itemprice)){
            validItem = false;
            priceField.set("v.errors", [{message:"Item price can't be null."}]);
        }
        else {
            priceField.set("v.errors", null);
        }
       
        if (itemprice<0.01){
            validItem = false;
            priceField.set("v.errors", [{message:"Item price can't be zero."}]);
        }
        else {
            priceField.set("v.errors", null);
        }
 
 
        // Quantity must not be blank
        var qtyField = component.find("quantity");
        var itemqty = qtyField.get("v.value");
        console.log("itemqty ="+itemqty);
       
        console.log("now check empty"+qtyField);
        if (isNaN(itemqty)){
            console.log("bad qty ="+itemqty);
            validItem = false;
            qtyField.set("v.errors", [{message:"Item quantity can't be null."}]);
        }
        else {
            console.log("good");
            qtyField.set("v.errors", null);
        }
        if ($A.util.isEmpty(itemqty)){
            console.log("bad qty ="+itemqty);
            validItem = false;
            qtyField.set("v.errors", [{message:"Item quantity can't be null."}]);
        }
        else {
            console.log("good");
            qtyField.set("v.errors", null);
        }
        if (itemqty<1){
            console.log("bad qty <1 ="+itemqty);
            validItem = false;
            qtyField.set("v.errors", [{message:"Enter an Item quantity."}]);
        }
        else {
            console.log("good");
            qtyField.set("v.errors", null);
        }
       
     
        return(validItem);
       
    } //validateCampingItem
})
 

campingListItem.cmp

<aura:component >
    <aura:attribute name="item" type="Camping_Item__c"/>
   
    <p>Name:
        <ui:outputText value="{!v.item.Name}"/>
    </p>
    <p>Quantity:
        <ui:outputNumber value="{!v.item.Quantity__c}"/>
    </p>
    <p>Price:
        <ui:outputCurrency value="{!v.item.Price__c}"/>
    </p>
    <p>Packed?:
        <ui:outputCheckbox value="{!v.item.Packed__c}"/>
    </p>
</aura:component>
 

CampingListController.apxc

public with sharing class CampingListController {
 
    @AuraEnabled
    public static List<Camping_Item__c> getItems() {
       
        // Check to make sure all fields are accessible to this user
        String[] fieldsToCheck = new String[] {
            'Id', 'Name', 'Quantity__c', 'Price__c', 'Packed__c' };
 
system.debug('fields: '+fieldsToCheck);
       
        Map<String,Schema.SObjectField> fieldDescribeTokens =
            Schema.SObjectType.Camping_Item__c.fields.getMap();
   system.debug('map: '+fieldDescribeTokens);    
        for(String field : fieldsToCheck) {
            if( ! fieldDescribeTokens.get(field).getDescribe().isAccessible()) {
                throw new System.NoAccessException();
                return null;
            }
        }
       
Hope this helps.