I like the idea of booking activities they could do there. Or, it'll be after the fact but you could put together photo albums of the trip for everyone. (I like to use iphoto, easy to order through Apple directly, great for adding in text too for fun memories and stories. Just order multiple copies of same book). Conduct interviews and take notes to add into the book, and set up a certain photo op for everyone while you are there so that they know what's coming. Or if youre video savvy you could do a video.
Along the same lines, you could gather up old family photos and make a book for everyone. It would be fun to look through them together on your trip. Do a little reasherch and include some family history (ancestor.com might be a good start). If you keep them small I don't think they'd be too heavy to travel with.
Or gift certificates are good. You could look up local restaurants in their towns and get them ahead of time. One of my favorite go to gifts is a "night out" (gift certificate to a local restaurant and movie theater). It's a little more personal than just gift cards to big chain stores when you get something specific to their home town.
One year my uncle got everyone 20$ worth of lotto scratchers, it was fun to see who won what. But that might be state specific, so don't know if it would work if you're coming from different states.