That is a neat idea for an adult craft project, especially when you add coffee to the mix! ;) The ones you painted are nifty. I really like the stormy sea one with the whale.
Perhaps one project you could do since you mentioned seed saving, is a small starter window sill herb garden.
Another idea could be candle making as you mentioned soap making as a possibility.
I don't know if this would work but, maybe a learning workshop on native plant identification and foraging.
I think all the hard work and effort you put into your library is great and I hope you are successful with your summer programs! :)