I might suggest a blanket chest or a memory box. Two ideas already given above. If you do go with a card for a future project you may want to put a few ideas on there. Dining room table hall table etc....give them a few ideas. Another idea is to make a small memory box for them with a card inside to build a bigger piece of furniture in the future. It all depends on how much you want to do. Do you want to make a big piece or something smaller or a few something smaller. A box and a few picture frames.
I did the same thing as someone mentioned above with the picture and border for people to sign. I still don't have a frame for it.
Good luck and keep us updated.
Greg