Battery cut off switch

For a trailer, the breakaway braking system will (or at least should) always be wired directly to the battery, bypassing the cut-off switch. Of course, it doesn't consume any power unless activated.

Other things are entirely up to the manufacturer. As Bob said, many have at least the CO and propane detectors unswitched, and possibly a few other odds and ends (the memory wire for a radio, for instance).

It seems that most mfg's leave at least the CO detector hooked up. When most people install them they do it close to the battery and cut off everything.