Only Baptists baptize, and it's literally dunking your whole body into water. We had a huge tub behind the pulpit, it was about three feet deep and 12'x8'. I can't imagine that happening in a Cracker Barrel parking lot, unless it's one of those pool-in-a-pickup-truck-bed situations.
"Giving your life to Christ" is basically what it sounds like. An often emotional moment in which you make a personal commitment to the Biblical idea of Christ and his teachings. Think of it like an epiphany.
Edit: my bad guys, I got the terminology wrong about which sect of bigots have wet tshirt contests.