OK, spare parts if you plan on out of a van living for ten days or two weeks:
1-2 each? Front 21"/rear 19" tubes (how many is up to you).
I would get the IRC heavy duty tubes. 80/100X21 and 110/90X19
2-3 Air filters oiled and ready to install, gives you a 3-4 total. I use twin air and UNI cleaner/oil kit when out and about.
1-2 Spark Plugs extra (I run the iridium but they are 9.99 each over 4.99 for regular)
1-2 Bottles of Honda HP Trans oil, Trans takes 750 ml per change
4-6 Bottles of Yamalube 2-R 32oz (premix two stroke oil)
2 drain plug seals OEM
1 Bottle coolant (engine ice)
1 10 scoop paddle tire 19". 10 scoops is better than less and I have no idea on type/make, I don't do the dunes...
You will need to look into a flag mount and flag for the dunes. I might have a flag from my ATV days. I will look.
If you would like to buy my rear extra rim off me no problem or just use it is fine.
Might need extra chain 114-116 links for the paddle tire to clear properly. (just a thought)
Brake and Clutch lever. Don't know how he did it but even with bark busters my son broke one. (just a thought)
2 5 gallon gas cans and measuring cup 20 oz min for 32:1 premixing 4 oz per gallon.
Tools:
L=large, M=medium, S=small
When you get here I'll steer you to inexpensive that are good enough. Check Harbor Freight online...
1 Box of latex gloves (L/M/S)?
Tire irons
Hand/plug in pump
Metric wrench set
Metric Socket set and a few extensions
Metric Allen wrenches
5 in 1 screw driver (or a set)
Pliers set with needle/dike/adjustable
JB weld (5 minute epoxy)
little sand paper/emery cloth
Zip ties (L/M/S)
Bike Armor:
Things to consider...
Radiator braces (works connection)
Skid Plate (Ricochet, Flat land)
Pipe Guard (moose)
Don't forget to tell him to bring the ding dongs.