I'm considering storing a few extra maintenance items for the X. Thing such as oil, oil filters, brake pads, radiator hoses, etc. I would like to know what other members may be accumulating for maintenance items.
All I carry is a quart of oil, as far as parts for the Xterra. I do carry a tool bag and extra repair equipment, which you may already do if your considering extra parts. If not I'd focus most on carrying a well stocked tool kit before random parts.
I wouldn't see the need to carry regular maintenance items like oil filters or brake pads, that stuff isn't likely to go out on you all at once, and if for some really strange reason it does, it can be obtained easily at the nearest auto store and in the case of general maintenance, heck you can put that stuff on in the parking lot. Most of the time, if something goes, you probably won't have one with you, and it probably won't be handy. Better to try to limp home without it than pack a truck full of parts, and if you can't limp, your getting towed anyway.
The only time I see packing extra parts as prudent is if your out in extreme off road conditions, and you have a spare axle shaft, and maybe some U-joints. Even then people who do that generally know where the weak points in their rig is and try to anticipate what is going to pop first under pressure.
If I were to go all out, in addition to oil I would carry water (can be used as emergency coolant) brake fluid, power steering fluid, some gear oil for the axles, and maybe a spare belt. In the event you find something low or leaking, and you can try to patch and stay ahead of the leak until you get back to civilization. I carry this kind of stuff routinely for my Bronco, which is a much older and less reliable vehicle overall, but also a lot easier to hack on in a pinch.
There is also some tape I read about for fixing hoses, safety tape or something. I haven't bought any yet but I plan to. I'd pack that instead of trying to pack spare hoses if it works. Sounds handy.