Clean a toilet: Toss in two dissolving antacid tablets, such as Alka-Seltzer, wait 20 minutes, then brush.
Remove a stain from a vase's bottom: Drop a tablet in a little water and let it sit for several minutes. Wipe and rinse.
Soothe a sting: Dissolve two tablets in a glass of water, then dab on bug bites.
Impress a kid with a fun science experiment: Pour water into a plastic 35-millimeter-film canister until it is one-third full, drop in a tablet, replace the lid, and quickly place the canister upside down on the ground. Stand back. In 5 to 10 seconds, the gas pressure will make the canister pop its lid and shoot several feet into the air.