air filter, air filter cleaner, air filter oil, fuel filter, fuel line, throttle cable, chain, any hardware that sticks out below the chassis (grinds down)
Chassis: front/rear bumpers on occasion will get ground down (front bumper on the bottom lip, rear bumper can grind against your tire). Axles get bent. Kingpins, kingpins get bent about once a year due to bumping something/someone. Rear axle bearings wear out. Rear axle gear teeth wear out.
Engine: ALWAYS keep a spare piston/ring/wrist pin/bearing. You never know and it usually isn’t good. Spark plugs, buy them buy the pack for use jetting. Seals/gaskets, every time you take the cases apart it seems the gaskets get a little damaged. You might want to consider a spare crank assembly. Definitely need extra springs and viton rings for the pipe/manifold. Spare base gaskets for the cylinder.