I did a bunch of variations on the re-useable cotton coffee cup sleeve because STITCH was trying to sell these for a while at our local coffee shop. I still have these 8 at home to try and sell next year, perhaps. I'm not much of a coffee drinker myself, but I would definitely carry one of these around for my occasional hot chocolate or hot tea :)
It was actually really fun making up all of these because it's like making a bunch of tiny swatches that are useful! I have this beautiful book of crochet motifs that I picked up at my local used book store, and I tried out a few different patterns from there. I even tested my technical skill with some Tunisian crochet and some crossover/front post stitches.