It's really going to depend on what kind of off-roading you do and how your vehicle is setup. If you do a lot of rock crawling that can take out parts with a vengeance, have a lift and a locker, you would really want to carry quite a bit of spare parts with you. My parts box includes cotterpins for the front end, a spare idler arm or two, tie rods, a front brake line and banjo bolt, can of brake fluid, line seals for the brakes, lug nuts, etc. As you hit the trail you will find things that you break or damage and it will prompt you to carry parts for the stuff that appears to be an on-going problem. I actually broke a brake line on the road when I bounced the truck over a curb in a u-turn and it kicked up a piece of cement I didn't see. Had I had a spare at the time, it would have been no big deal. Now I carry a front brake line and bleeding tools everywhere I go. So it is all a matter of experience. As time goes by, you will figure out what you need to carry.