I always hope I get a bow in the arena. With just a little power draw (4 should suffice, is what I start the game with) you just need to hope you don't get swarmed right at the beggining. I then make my way to the middle, steal a board and sword in case something goes wrong, and just headshot everyone as they appear. Then as the last 10 spawn at the same time I move to a side, let them kill each other until three remain (who inevitably all decide to kill me) and finish them off as they run in a straight line at me. Shield guys take two shots to the knees, but there's still plenty of time to kill them all.
Pity the bow is, from my experience, the rarest weapon to get. Shoots your proficiency up very fast though.