I carry a v. small handbag and always seem to end up having to carry a plastic bag by the end of the day. So I made a tote that folds up really small in a pouch and can be put in my handbag until needed. Here's a photo of it folded up next to my handbag: http://photos14.flickr.com/14088786_9b35e7af56.jpg
and here it is unfolded: http://photos14.flickr.com/14088787_def4fe63b5.jpg
and with a couple of magazines, a bath towel and shoes in it: http://photos11.flickr.com/14091269_f86c440adf.jpg
I made it from a headscarf, the square silky (but 100% polyester) kind, so it squishes up really small yet holds loads and is pretty strong. One square was exactly enough to make th bag and a little pouch to put it in with nothing left over at all. This was really cheap to make as you pick up those scarfs at thrift stores for a buck or less and they come in really cool colours and patterns. I've made loads more to match different outfits.