I have the necessary three holes to mount my big vice to my table drilled and tapped on one corner. The vice usually doesn't live there, but I ran across a need for it once, so I made it permanently possible.

Shelves? I didn't, but I also needed it to be able to slide over other tools/items and therefore take less space when not used. If I didn't need that, I wouldn't have gone with shelves. I would have gone with something like this underneath to hold welding/fab specific tools.