Simple! Pop a couple of caps on the nipple BEFORE you leave home. Then carry your rifle in a hard case where no moisture or oil can get into the breech area. Do this AFTER you have dry-patched it as Mike suggested.

The reason why this is required is because merely dry-patching the bore will NOT ensure there's no oil or moisture in the breechplug-drum area, nor will it ensure the flash channel is clear. Whenever you pop a cap or two on the nipple before loading, always hold the muzzle down and near a light object, like a leaf or cleaning patch, and observe that the blast from the cap is moving this object, proving that your flash channel is clear. If you have a rifle with a removeable breech plug like these newfangled inline contraptions have, remove the breechplug and dry out the flash channel and nipple thoroughly with a clean, dry patch and you can skip the cap-popping drill completely.