I carried two in my Taco when I ran the Old Mojave Road alone in '04. Stock tires and two factory spares (one under, one in, the bed). Didn't need either until I had completed both the OMR and gone up over the Clark Mountains by way of Coloseum Gorge. All my offroading was done and it was almost all pavement for the remainder of the trip.
Coming back down through the Mojave National Preserve I pulled off the Kelbacker-Sima Rd. to look at one of the NP signs and apparently picked up some glass.
Only consumed one spare that trip but, I'll tell ya, alone in the desert, two spares is good peace of mind. I don't think I'd have done the trip alone w/o them. Of course, that's not to say I had all the other appropriate spares but I've only been on the forum for a limited time so I'm working on it.
I'm currently considering having my Sonoran Steel bumper modified to carry a heavy-duty, bolt-on, swing out tire carrier. This way I can mount up a second spare for trips but not have to carry arround the extra weight driving to work every day.