Well you�re going to need mics for the guitar and bass cabs and then depending on the amount of toms and cymbals and bass drums for the drummer your going to need mics to cover that. Allot of cable and a snake can help. If you can, monitors for the musicians and a monitor board(not really needed, but nice). A sound board that covers all your channels. Also depending on your sound system you may need multiple amps and power.
The main thing to know was already said. The musicians will want it loud but they don�t hear the mix. A nice bass beat and clean guitar solos go allot better with vocals then just pumping up the singers vocals and all you hear is screaming with music in the background. You can have a small sound system and still have a great concert if mixed clean rather then loud.