As some have said before.. walking/jogging/running.. situps.. pushups.. that's the poor man's gym right there and it works.

There are different ways you can do pushups widearm, close hand, regular, and more advanced. The same with "Situps", you should actually do crunches which work your abs, situps don't really they work your back. Try alternating how you do them say crossover your chest, bring your left elbow to your right knee and then vice versa.
I'll see if I can't get a buddy to do up a workout plan for you that don't require any exercise equipment, (he's a personal trainer).

I've been the military for 9 years (Army 4, and Coast Guard 5) and I've always stayed in great shape without any need to workout equipment. In the army it was a rare day that we touched weights, 99% Run/Situps/Crunches/Pushups/Pullups/Dips

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