US airlines do not have to have lifevests or rafts if they don't operate over the ocean (I think there's a small amount allowed for coastal airports.)

If you land in a lake, it's just you and the seat cushion.

By the way, Southwest has just introduced lifevests on its aircraft, to take advantage of routes over the Gulf of Mexico. There's some discussion in this in the Southwest forum, as the F/A briefing now includes the lifevests on all flights, not just those operating over the ocean.