h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

A great idea for a cold compress that I find really useful is this. Take an old face flannel, wet it thoroughly [but not dripping] with cold water, fold it into a square then place it inside a greaseproof bag and store in the freezer.

I have 2 of these stored and they make great compresses, as they mould to joints once they start to thaw out. I just wrap them in a teacloth and apply to the affected area. We also take one of them in our small coolbag on days out. Not only do they help to keep drinks etc cold, but are also great for a refreshing cool wipe down when you're overheated. Also a very good way to use up old flannels!