If your swim step can accommodate it, you can either buy or build a bait tank.
On my funship, I took the white-trash approach and build one out of a plastic garbage can which I strap to the swim step. I mounted a pump on the transom with a pipe to keep water flowing through the tank for aeration. Power currently (pun intended) comes from my anchor light receptacle - I bought a cheap pole from Wal-Mart and cut it short while using the wires to connect to the pump
. Admittedly, it's a bit embarrassing and the wife would never allow it if she saw it....How about something like this: http://tinyurl.com/yengejp