There was a spare on our older gassers, both 16" and "easy" to change. 50 years ago when I was much younger I spent a year in a tire shop where we did a LOT of commercial trucks including road service. The current rig has 22.5 radials and though easier to change the the old bias plys I knew they would be beyond me.
We have travelled all of North America from Alaska to the Belize border in Mexico and have never had a blow out in the Atasca. CHECK TIRE PRESSURES BEFORE EACH TRIP and check tire temps at each stop using an IR gun.
In the Commander many years ago we had a blow out but even though we had a spare I called the road service.