This one was fairly easy. I don't actually have any medicine cabinets. I just have mirrors above each sink. Luckily I have a fairly large linen closet in my master bath. However it holds everything from towels, to medicine, to kleenex, to extra candles.
I do have some stair stepped shelves in two places but everything was just thrown in there. Once again, I blame my husband. He buys everything in bulk (hence the 8 boxes of kleenex, 4 bottles of hydrogen peroxide, 6 tubes of toothpaste, 10 bars of soap, etc - although I have to admit that the body soaps and lotions are mine). He is also lacking the organization gene so everything is just put in any open space. I was mainly focused on the the lower three shelves and the floor. I pulled out old items to dispose of and grouped all the like things together. I have a ton more space now and I even cleared off some of the floor area.
I'm really not sure where all the space came from because I really didn't throw that much out. I did open all the multi-packs and throw away the packaging so that helped.