After all the normal prep to ensure good ignition, I hunt. If not fortunate enough to get a shot, I pull the cap, put a small piece of leather btwixt the nipple and the hammer (or under the frizzen in a flinter) and leave the gun stored outdoors. Next morning I pull the nipple, work a pick in the hole to loosen powder a bit, and dump a tiny amount out, replace it with a bit of fresh powder from my priming horn, replace the nipple, and set out to hunt again.
In over thirty years of hunting with frontstuffers this has never failed me in the field!