The items are generated via AJAX request. When you connect to a page a javascript script is executed that makes some extra http requests to retreive some json data. However scrapy does not execute any javascript so you need to manually find and call those AJAX requests.
See related issue: Can scrapy be used to scrape dynamic content from websites that are using AJAX?, to see how inspect network traffic and solve such cases.
In this particular case you can see first xhr
requests that is being made returns a huge json file with all of the item data:
http://bananarepublic.gap.com/resources/productSearch/v1/search?cid=1055063&isFacetsEnabled=true&globalShippingCountryCode=&globalShippingCurrencyCode=&locale=en_US&
As you can see url takes some arguments, most importantly it takes cid
which stands for category id and other arguments are mostly for calculating shipping prices, so if you don't care about those this works just as well:
http://bananarepublic.gap.com/resources/productSearch/v1/search?cid=1055063