Have a read of this thread to find a tire (or 7).
From what I have read, most people carry one front spare, mounted and balanced. If you lose a front, you can change it yourself and drive to get it repaired.
If you lose a rear tire, you can take the wheel off, and limp to a service center on 5 tires. If you lose another rear, remove it, balance out the rear with one tire on each side and crawl to the service center.
I have considered keeping a new unmounted spare rear tire on board in the event that a local service center cannot find a replacement, or it takes them days to get one, and the cost! This way, you can be in and out, but is it worth the weight? Maybe.
At least if you had to order a tire and wait, you wouldn't be left without a place to sleep...