The obvious thing is electrical wiring:
power, for lighting obviously; also, any USB chargers, cigarette lighter outlets, inverters, rope lights in the cabinets, fridge controls, range ignitor, water heater controls, pump, furnace
- 120v power, usually less important but if you need to replace deteriorated wire now is the time to do it. If you're upgrading to 50a service do it now. Might also pre-wire for an electric water heater and electric heat if you have aspirations for either
- A/V connections
- instrumentation, like tank gauges or a integrating ammeter (battery capacity meter)
- solar panels
- tail, turn, backup, and running lights
- backup camera
- thermostat, particularly a consideration if you're thinking of relocating it
- any outside lights you plan to add in place or in addition to the usual "scare light"
This is also a good time to complete any exterior sheet metal or window repairs since you can use buck rivets while the interior panels are off.
It is also a good time to replace or overhaul any running lights if you're going to do that.