I like to do as much science as I can using everyday materials. When it comes to basic chemistry the vinegar and baking soda reaction is one of the easiest, safest and useful you can come across. Wayne from www.apple-cider-vinegar-benefits.com has a great page on simple experiments from basic volcano building, to stoichiometry (using a balloon) and demonstrating endothermic reactions (but you’ll need an accurate and fast thermometer).