I had this offer on 4 of 5 cards. If you don't want to buy something outright the iTunes app lets you send gift cards though there seems to be a $10 minimum. Remember to update your account settings with your Amex card number before buying the gift card as the gift card process doesn't ask for a credit card number.

Once loaded into your account iTunes credit can be used for iTunes, iBooks, and App Store purchases. It will also be used to pay for monthly Apple Music and iCloud storage subscriptions.