A neoprene knee sleeve is just like a knee-warmer for biking only heavier. It'll have a hole for your kneecap to stick out of. I have one for days when my knee is grumpy. They really don't do anything but give your knee a little squeeze of support and keep it warm. If you don't already have one, I don't know that I'd bother to go buy one if they're expensive at your pharmacy - the squeezing pressure might be uncomfortable if you've got a lump on your knee!

But ice could be a very good thing.