To get the secret Rocket Pack for any character, find the rotating platform with the jump on it (which occasionally raises into the air) and go off the jump. You will obtain a Rocket Pack for a short time, but will still be able to use your other weapons (except Gunship, which is also a flying weapon). Use this with the Cluster Bombs weapon to rain bombs on your opponents, or with the Machine/Tommy guns to become a turbo-charged Gunship.