Are there any good workouts (without weights) to work my arms?
Planking is really good for your arms. I do one where you plank on your palms for about 10 seconds, then go down to an arm plank for 10 seconds and rotate. Also, the push-ups where you go all the way down to the floor and come back up work well too.
Push ups and pull ups do not take anything but your own body weight. They are also some of the best exercises to do for your arms.
got a college backpack? use that
Diamond push ups.