Several posters have brought up a good point to know what is recommend for your car. If you have all wheel drive or limited slip differentials, usually on jeeps, suvs, trucks, and sports cars. You may need to use a full size spare or use the spare only on one end of the car.

One of my cars has a doughnut spare, the spare can only be used on the front axle. The rear axle has a limited slip differential and it can be damaged by using different size tires on that axle. And it is an expensive repair.