not enough info. How many loads? Total amps to be drawn? Electronics or lights or both? How far from battery?
google "marine wire gauge chart" you'll find a lot of info.
here's one
http://www.westmarine.com/WestAdviso...e-And-Ampacity
I run 8 gauge to the panel in my cuddy and it is overkill.
Also, I have a 30 amp fuse at the battery terminal. Very important to fuse the feed to the panel at the battery.
I'll never draw 30 amps unless I accidentally touch an aluminum landing net across the panel but if I do, the fuse will blow before the wire melts.