A couple games we have played.
Wolf is a fun game (you can look it up).
My buddies and I tend to drink a fair bit on the course and do "every 2 beers you drink, you get a stroke knocked off". You can modify that however - you get a mulligan, etc.
There are challenge holes - like closest to the pin or longest drive - and the winner gets to negate another's shot. For instance, if my buddy gets closest to the pin and on the next hole I drill a drive, he can say, "negate" making me rehit. If I hit it in the fairway (or make it on the green, make the putt, whatever) he adds a stroke. If I miss-hit, I simply play that shot.
There is best save out of a bunker, plus every time someone goes bunker to bunker (or in the same bunker) they owe a round at the end.