I carry spare fuel using a Kolpin bracket and can. I mounted it off the back of the rear rack. With my rear storage bag in place it doesn't look too obtrusive, although when I take the storage bag off (hardly ever) it stands out like a sore thumb.
For spare parts all I carry is a spark plug and a belt, although I don't relish the idea of changing a belt on the trail.
My tools consist of a small 3/8 drive socket set with sockets that fit both metric and SAE, a screw driver handle that accepts driver tips from straight to phillips to torx bits, the machine's tool kit, a cresent wrench, pocket knife and multi tool.
For accessories I carry electric tape, duct tape, cable ties, a tow strap, a squirt bottle cap to screw on water bottles to flush crap out of the radiator fins, a folding saw to cut smaller trees/branches and a chain saw chain (not looped) with rope on each end to cut larger trees.