Justin liked this idea as well, and we have LOTS of baby food jars yet. Stained glass votives.
You just mix 1/4 cup of baking soda, with 4 Tbs. water, and a few drops of food coloring into a dough. Put your little treasure in it and roll into a ball so that it looks like a stone. That's all. Just let them sit in the open air to dry overnight. (hide a small treasure inside)Personalized memory Game. Thought this one had potential.
The next morning you can just put the fizzy stones all in the GladWare box, and put it in a gift bag along with your bottle of vinegar.
You'll want to have a clear measuring cup or bowl handy so that you can pour the vinegar in and watch the magic happen.
The vinegar does lose its potency fairly quickly though so after doing a stone or two, you need to dump out that vinegar and get more before adding another stone.