My dear sweet MIL, of all people, told me about drunken gummy bears, they sound so much better and easier than Jell-O shots!

Maybe you could get some silly hats or the headbands with stuff on them like horns and antennae, etc. and maybe set up a photo booth area so everyone can set up their own silly pics themselves. I'll bet wedding sites or Pinterest will have plenty of how tos for those.