Consensus is two!
You cannot go anywhere worth going without at least 2x spare wheels.
Plus...
1. You are going to need an easy method of loading and unloading those heavy wheels from your vehicle without breaking your back
2. You need the correct tools to loosen those darn wheel nuts! (there are plenty good manual tools available for this but we are taking it a bit further on our vehicle: I am busy installing a 40L dedicated air tank that can be linked to another 10L air tank, the smaller tank currently supplies my air suspension, plus a heavy duty 220v compressor to give me 10 bar worth of pressure off which I can run an air impact wrench)
Why give up the luxuries when in the bush.... the reason we are building these vehicles in the first place right?