Most of this is common sense for any long trip, but it'll be a horrible mess if you are stuck 50 miles from the nearest place that has a tow truck, which is already busy towing the other people with breakdowns.
If you take it to a mechanic and there's a problem, better to deal with repairs now. Give them time order any special parts, let the repairs settle in before the trip.
I'm doing maintenance myself, here's a few things I'm doing:
- Check and replace brakes - important due to riding heavy on twisty and steep roads
- Change oil from 5W-30 to 10W-30 for better high temp performance
- Replace/clean air filter and oil filter
- Inspect tires, pressure and alignment
- Replace worn shocks
- Check transmission and transfer case fluid
- Check radiator condition and coolant level
- Inspect fan blades
- Inspect battery and belts
- Check high and low beams, brake lights, turn signals
- Track down any squeaks or rattles
- Test and recharge air conditioner
- A couple quarts of engine oil
- Spare air filter
- Jug of coolant
- Fire extinguisher
- Can of gasoline
- Bottle of transmission fluid
- Bottle of windshield washer fluid
- Plywood for jack stand - push the car up, not the playa down
- Battery jump box
- Socket set, screwdrivers, and wrenches
- Air pump
- Spare fuses
- Spare light bulbs
- Liquid Wrench
- Rags and pumice hand cleaner
- Tow strap