Dude, in that environment, do the ******** things that make anyone reasonable ban items and bad stages. Camp in stages that provide natural cover, be the first to get to items, and kill them with final smashes. But expect a lot of random crap to happen to you as a result of such a horrible tournament rule-set.
On the plus side, there's no way anyone good would go to something like that. Sonic is good for getting items first and kills with his final smash just about every time.
So basically, there's a reason for the bans, exploit them to make the tourney director realize the idiocy of their rules.