I'm a beginner bass player, and my band and I are going for the battle of the bands competition in my home town. I am very confident in my own, and my mates', abilities. I just need some advice as to what to do, or more importantly, what not to do.
Bring spares of everything and anything that can break or fail. Bring a written set list. Act professionally. Most importantly - Have Fun!!!
You say you are a beginner. So, come early, yes to extension chords, etc. Smile and have fun. Enjoy the experience.
Load your equipment in your car/van/etc. Drive to a friend's house, set up and play your full competition set as if you were at the real event. No cheating. How did the test run go? Did'ja make notes about the stuff you wished you had brought or done, etc? Have fun.
Keep people off the booze before the gig. One crap-faced link makes the entire chain suffer. I would say keep 'em off the dope but the guys who smoke all the time are usually better after smoking up, so play that by ear.