A bandanna is possible the most useful bit of kit anyone can carry.

They are water filters, bandages, field expedient socks (portyanki), and loincloth (emergency replacement underwear or swimsuit). A string around the waist, possibly a narrow strip ripped from the bandanna and twisted to form a cord, and a narrow rectangular cloth formed from the larger piece by folding or cutting.

My favorite are simple unbleached cotton muslin sold as a 'triangular bandage', that are typically about 30" square, and sell for a bit more than $1 each and often come with a couple of cheap but handy safety pins. You can dye them any color you like but the natural off-white looks good to me. I'm not willing to pay an extra $5 to get the OD green version.