Don't worry -- my blog has not become a satellite office for the home shopping network and this is not intended as a sales pitch, but I got a pack of these cute little disks as part of a gift exchange and promptly discovered how useful they are for watercolor painting.
The disks are about the size of fat nickels and weigh almost nothing. Wetting the disk allows you to unroll it. The cloth is a decent size -- about 9" x 9" -- and you can wipe your brushes on it or use it to blot up paint as you lift it from your paper. You can rinse it clean, squeeze it damp dry and it's good to go again. It's sturdy enough to last for multiple painting sessions and it doesn't appear to leave lint, unlike facial tissues. Plus, they're cellulose, so they're biodegradable. I'd bet that a few of these tossed in your plein air kit would be enough to keep you going for hours.
My friend picked up this 12-pack for a couple of bucks at The Container Store, but you can buy them in bulk packs of either 100 or 500 online. Tell them Chris sent you!! (joking, joking...)