Use an iTunes gift card to pay for something I bought yesterday and avoid a credit card charge

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

In any of the common scenarios in which you store your Store credentials on devices under the control of others, it makes good security sense to have those be different from the ones you use for iCloud.

For example, it is common to share music among family members by using an Apple ID for purchases on all of the family's machines. If that Apple ID were the same as the one you used for iCloud, then (unless you can be sure that all family members have secured their machines) anyone who got his hands on one of those machines could potentially gain access to your e-mail, calendar, and documents (and, in typical configurations, could even log on to your machine if he had access to it).