You can give yourself extra health by pressing CIRCLE (default insert credit). Makes the Red Cross look like a laughing joke.

You will need a PS2 multi-tap if you involve three players. Each controller port corresponds to one of the monsters in the game. Starting the Rampage game with a controller in specific port relegates you to playing that particular monster:

Port 1 - George (Gorilla)
Port 2 - Lizzie (Lizard)
Port 3 - Ralph (Wolf)