Caffeine only works for so long, you need intermittent hard exercise. Your pace or reps and stuff will be shit but that isn't really the point, the point is to keep you up. Don't do walks, instead do runs, pushups, that sorta stuff. If you have a machine that won't kill you if you drop it that should be okay, but I would avoid weights generally.

Also, make sure to get daylight and fresh air. Being awake during the day will help your body think it shouldn't sleep.