Always carry two wet-wipes in your camera bag. Aside from cleaning out wounds (see Cheap Trick #27), we photographers like to get down on our hands and knees to get that perfect shot. When you’re done you’ll probably want something to wipe the sticky stuff off of your camera, because you can’t douse it with your water bottle! That you use on your hands!
[Also be sure to replace these once a year, nothing like a dry wet-wipe.]