for USF games last year, i always brought a laptop and i already have a hardwired power inverter. I had a patch panel of outputs from my 4 channel amp into RCA connects on a board. The 4 bookshelf speakers we used for tailgates (placed them on car roofs with 20+ feet of speaker wire, had RCA ends terminated on them so that when we got to the lot we simply pulled the shit outta the trunk, set my laptop on top of my sub box, plugged the speakers into the patch panel and threw the RCA to 1/4 inch laptop cable into the Amp imput.
helped to have a metal paperclip to bridge Batt + and Remote for the amps.
took 5 min to setup, ran the whole car speakers, the bookshelf speakers and the sub with no real work. got loud and we also threw a Mic on the laptop for starting trouble with other teams.