As far as ***MUST HAVE*** spare parts, I don't think there are any in order to get off the trail, but if you are looking for the luxury and convenience of being able to repair your rig on a remote trail and keep wheeling, then I might have a few suggestions only based on what I've already broken on the trail: axle shaft u-joints, drive-shaft u-joints, ball joints, tie rod ends, and a rear axle shaft. Other than that, it is up to you, but as mentioned above, I suggest you have the proper tools and knowledge required to repair, or at least temporarily-fix your rig to get you off the trail.