Baby wipes will save your life.
The term "baby wipes" refers to any of the moistened napkins that one would normally use to clean a baby's backside when changing his or her diaper. They are similar in design to wet-naps and moist towelettes. They come in a variety of brands, scents, sizes, and with varying amounts of lotion already added (or not added) to them. These little wonders usually come in a plastic dispensing container that functions much like a tissue-paper box, although the wipes themselves may or may not be layered in such a way as to leave another wipe in "ready" status when you pull one out.
These little things are very useful cleaning tools. They are much more efficient at cleaning food from a baby's face, hands, and clothes than napkins at any restaurant. They are also much more sanitary than any public restroom. There are uses beyond those specifically geared towards babies though, which make them a potential buy for non-parents.
Baby wipes, or wipies as they are called in my neck of the woods, are great for quickly treating any organic stain on your own cloths. They work great for cleaning kitchen surfaces if you are pressed for time. I'm sure I've used them in many other exciting cleaning situations, but you get the picture.
Finally, and this is the real kicker, they are eminently portable. If you carry a bag of any kind around with you, you have a place to put them. Plastic baggies will do just fine, but I suggest that you get one of the slim carrying units that are readily available in any grocery store. If you do end up buying baby wipes, you'll no doubt see a pack of them that has its own "travel case", so make sure and get one of those the first time you buy wipes. Otherwise you can get them in refill packages without buying more hard plastic containers.