My approach is the same way I approach anything I take seriously. I maintain the routine. I always clean in a manner I can do in the field. In the field, I clean the same way I do at home. It isn't like you need anything special. All my ramrods are threaded. All that is needed is a jag or worm. If you are going somewhere that long, you will have water, or likely access to it. However you clean at home, just do that in the field.
I'm speaking from personal experience here, not unfounded opinions. It is very common for me to go to our farm, where all I have is a fish house to sleep in, and shoot the day before a hunt. I'll then clean as I always do, except I get the water from a jug, not a faucet. I did it this year too. I shot the day before for practice, cleaned that night, and then proceeded to hunt 5 days, shot a deer, cleaned again, hunted the rest of the days, and fired the shot off the last night. I use nothing but room temperature water, patches, and oil. I do have the luxury of heat, so I dry my barrel over the heater. I've also used the sun on a early September bear hunt. I even used the dash heater of my truck one time when I was testing out clean bore shots at the range. I've never been anywhere I didn't have a stove, or at least could start a fire. If I was way out somewhere in the fall or winter, with only my small alcohol stove, didn't want to start a fire for some reason, I would seriously consider doing nothing but running a spit patch, followed by a dry patch, and trusting the patched ball to lube the barrel. I've done that too, and real blackpowder, especially in cold and dry weather, you can get away with it for at least a couple weeks.
Edit: One thing I forgot to mention was that I'm speaking of caplock guns. I always, no matter what, remove the nipple and make sure that is good and clear. I make sure that the channel is completely dry before I thread it back in. I do not fire any caps before loading. If you really wanted to be anal, you could remove the nipple after loading. If there is powder there under the nipple, and if you can see the hole in the nipple is fully clear, then it will fire.