If you don't have any commercial waterproof matches on hand for your outdoor adventures, you can make your using shellac or clear nail polish. You'll just want a way to dip the top half of the match, including the head, and let it dry evenly.
Brian's Backpacking Blog suggests attaching a strip of double-sided tape to a cardboard box. Once you've dipped a match in, you can attach it to the tape, which will allow the match to drip dry. If you have a strip of corrugated cardboard, you can also insert matches between the strips of corrugation to speed up the process.
Another traditional way to waterproof matches is by dipping the heads in melted paraffin or beeswax, but the author at the source link below indicates that this method does not work as well as using shellac.
Camping Classic - Waterproofing Matches [Brian's Backpacking Blog]