Bumper Jacks?? You mean those one leg wonders that were guaranteed from the factory to slip and drop while you were trying to change a tire? or the tire iron/jack handle would slip and smash your fingers?? That MPOS??
Wee-ell,, collect enough of them and you can turn them into posts for around a vegetable garden, or stakes for a horse-shoe pit, or bury them in the floor of your news garage just before you pour the concrete and tie off the rebar and mesh to them. See, they can be useful, just NOT as jacks.
For that I went out and scored a 2.25T baby floor jack( portable) from the local auto supply store and fits and sits just on top of the spare quite nicely. The spare, being full size lays flat and leaves the pocket available to stash other bits. JUst me, being creative.