I have a full size spare. As others have mentioned, it fits (mostly) in the factory space after deflating. One thing I learned the hard way after the fact (or maybe I learned it beforehand and went ahead anyway) is that I can't install the factory hitch with the full size spare in place. The tire occupies so much space I can't insert the hitch all the way to engage.
I'm taking a trip in a couple weeks where I need to use my hitch-mounted bike rack (as in photo above) so I'll leave the spare at home. I will have my tire repair kit and compressor and will have to pray to the Rover gods that I don't need anything more than that. It's mostly on pavement - half on the interstate, half on a quiet rural island - so I'll take my chances.