I think you guys are a lot more disciplined than I was at meets.
I didn't really have a backup vault, so much as I had a handfull of vaults to choose from, depending on how I was feeling during warm ups and how each vault was looking the night before. Sometimes I'd go with a handspring front, sometimes a tucked tsuk, sometimes a layout kazamatsu, sometimes a layout kazamatsu. All depended on which one I felt like doing on that particular day.
First time I competed a layout tsuk was about 5 minutes after the first time I ever tried one (I decided to try it laid out during warm-ups, because I was overrotating it tucked. I landed it, so I competed it.) First time I ever tried a kazumatsu was at a friday night practice, and I competed it the following morning.
Floor was similar; I made up my floor routines on the spot at each meet, depending on how much out of bounds room there was at each corner, where the judge was sitting, and which skills felt good during warmup. (This works a lot better for guys than it does for girls)