If your buddies are tagging along, shooting over your decoys and using your equipment, which is transported using your vehicle, boat/trailer, then I'd tell 'em up front that you guys are paying all other expenses, including gas, motel, and meals. Any complaints about paying anything above and beyond gas, say that they're also helping to cover the wear/tear & depreciation on your vehicle/boat/trailer.
If they are too cheap to cover those expenses, after you've invested thousands in boat/trailer & decoys, I'd find other 'friends' or tell them you expect them to kick in an equal share of what all the equipment cost you and you'd all split other expenses evenly. Their choice.
Nobody likes a freeloader. Had a guy like that tag along on a caribou/moose/black bear hunt one year. He wasn't my buddy, but rather a friend of my brother's and a last minute addition to our party of four.
The extra body forced us to take two vehicles, with myself and my old man paying for the shot, (effectively doubling our gas costs) which tallied up to about $450 gas each, plus two weeks provisions and related sundries. Aside from his own rifle, the guy had zero equipment and showed up with a 10lb bag of potatoes as his 'share' of the grub.
In the evenings around the campfire, we enjoyed a drink or a beer, once the day's hunt was over and the firearms were put away. We'd all provided our own liquor, except the freeloader. He ended up drinking on our dime as well, as my dad felt sorry for him.
If we hadn't been a couple hundred klicks in the back country, I would've booted the cheapskate in the arse and told him to find his own way home by the time the two week hunt was up. The guy was an arrogant asshat and totally unappreciative, despite the fact that we were paying for his entire hunt! Those of us with licenses shared our meat equally, except the free loader. He took an animal thanks only to our efforts. He didn't even offer us a single quarter as thanks after all we did for him. Needless to say, that was his last trip with us.
Having those types of guys along on a hunting trip can spoil the entire experience. I learned my lesson and there will be no repeats. Everyone pulls their weight or they don't come. Period. You'll feel a lot better if you institute the same policy.