How to store unfrosted cake. Baked today and want to frost tomorrow.

I do this all the time: bake the day before, wrap well, frost the next day. Just wrap it up in plastic wrap plus either a large zipper bag or foil. then frost the following day. Once it's frosted I generally put in a ring of toothpicks vertically around the circumference and one in the center, all pointing up and projecting about 1-1/2 inch, cover the whole with plastic wrap (the toothpicks keep the wrap from touching the frosting), then invert a large mixing bowl over it until serving time.

Might be too late now but try to avoid storing it uncovered as it will dry out. Alternatively, cover and freeze.