I have 1'x1'x1' canvas boxes I got from Lowes. They're open on the top and have a little canvas handle. I keep all the hats, undies, aprons, hair ribbons, etc. in the boxes. Each doll has one or two (depends on how many hats they have).

My husband made me a pretty storage thingie to hold the canvas boxes, but you could put them on any shelf system.