Drill, mostly, and guarding spaces, then drill, some time off to polish equipment for drill, dinner, then drill, drill and sleep.

I'm kind of kidding, kind of not. I wrote this answer which goes into somewhat more depth, but depending on the ship Marines lived quite boring lives. They were allowed to learn the skills of the seaman, but didn't often do so, and did not often fraternize with the seamen (being understood that the Marines were there in part to guard the officers against the men).