Sulfuric Acid reacting with a wet sponge

It reacts really funkily with sugar and sponges. Also useful for nitrating stuff (in combination with a nitrate salt) if you can’t get nitric acid, which usually you can’t unless you’re a lab. Or make small amounts of nitric acid for etching or decapping electronics. Or any number of things, H2SO4 and HCl are the backbone of a lot of reactions. Need is of course a strong word here – I don’t technically need to do any of this. I like to do them, and I value the opportunity to teach my kids about chemistry in ways that don’t involve going "OMG this liquid turned blue! How much fun was that!" with the kids responding "Almost some".