Which US Apple stores accept iTunes Gift Cards?
You can use redeemed value from an iTunes gift card to buy from the following stores:


iTunes music, movie and TV stores for iOS, Windows and Mac
iBookstore on iOS
App Store on iOS
App Store on Mac OS




The only gift cards that are accepted at an Apple Retail Store are Apple gift cards. The Apple Retail Stores and the Apple Store online do not accept iTunes gift cards as forms of payment. 

You can not use redeemed value from an iTunes gift card to buy an Apple gift card or anything else from the following stores:


Apple Retail Stores
Apple Store on the internet at http://store.apple.com
iCloud yearly storage space increases
iTunes Match service