Add to your "must haves" fresh belt(s) for your vehicle.
Unless it is new, put the new ones on...shake the idler if present to ensure condition.
Put the used belts INSIDE the "new" belt package.
Make certain you have a breaker bar to hold the tensioner on that serpentine belt.
Actually do it yourself, so you understand the routing and what is driven.
Take a picture of the front of your engine in correct form. If you loose a belt, compare to it.
Radiator hoses can bite you in the tukus out in the desert.
7 years or older...spend the Franklin(s) to have them replaced.
A gallon of oil and trans fluid, proper stuff for your vehicle. Put a funnel in a "ZIPLOCK" sealed plastic bag with several paper towels. Wipe it out clean/spray with carb clean before each use. (Dirt granules are not kind to your engine or tranny.)
Always have "Marine Tex" with you.
(It can save your whole world. Holding tanks, water fittings, holes in the body from a branch/bird strike/scrape. Even will get you home with a bad valve stem on a tire.)
Age of your vehicle???
If older, have the front "flexi" lines well-handled/checked.
Better to replace them if in doubt (ANY cracks of any kind and they need replacing) than lose your ability to stop 1200 miles from home.)
Buy a 12V compressor to fill tires. Not the cheapest one, either.
Use it before you take off. Several times. Make sure it is reliable. (Bike tires, toad tires.)
Make sure you have an air pressure gauge that can hit every valve stem on your rig, including toad/trailer/dolly.
(LED lights are the cats a$$!!!)
4WAY lug wrench, with the right nut size wrapped with electrical tape.
(When stressed in the dark, it prevents rounding off a nut trying the wrong size. They should fit TIGHTLY.)
The ones that come with your van are GARBAGE. Trust me on the 4 way. (Even when calling road service...they can show with missing tools. That 4 way has saved me hours on the roadside.)
Learn how to put that piece of oak for the jack and a rock under the 4 way...so you can use BEEF with your feet to remove stubborn lug nuts.
Speaking of lug nuts...even if new, it would be worth gold weight to have them coated (thinly) with never seize. Mark the lugnut location with a sharpie marker or tractor trailer indicator. Once torqued at the shop, if they move, you can see it in a split second when fueling.
Not sure of your abilities under the hood, but complete hand tools (screwdriver set, deep sockets, breaker bar (you bought for the tensioner...) magnet on a telescopic "antenna," and a good bottle or floor jack. (Screw the one they give you with the van.)
Add to that jack, a few OAK boards that will give it footing in the sand. It could save your life in the desert. A sawmill will be your friend for these. Slab wood with bark is fine. 12 inch long, 5 inch wide minimum. Get four of them.
If traveling in the cold, (Cabellas or LL Bean has nice ones) get yourself a snowmobile suit or coveralls with insulation.
Never put yourself in a cold situation you are not clothing-ready for.
Blah blah blah...pardon the ranting. Hope a few of these clicked for you or gave you ideas applicable to your own situation..
(Trust me on the jack, 4 way and Marine Tex though.)