First, check with the organizing group at your church, as sometimes gift cards are not allowed ... as they want "real" gifts.
For any gift cards, unless I know it's something the individual "really" wants ...
I think it's important to be sure it offers lots of options. While a book store gift card may be good for many, for some it may be less than appreciated ... unless the book store offers a lot more than books, and then there are many options available.
For example, one year, my sister gave me a gift card for Sears ... guess what? I had a hard time spending it, as I really did not want anything at Sears. I eventually spent it, but sadly, not on things that brought any "joy" to me!
I really like
Tartan's idea of a super-sized chocolate bar ... who wouldn't be thrilled with that?