I use the 3 drawer plastic containers you can get at Walmart/Target, etc. Think mini version of those big plastic containers for the toys on this is a small one that can either go on the countertop in the bathroom, under the sink, or even in their room.
http://www.amazon.com/gp/product/B002BA5F6Q/ref=pd_lpo_k2...
I put all scrunchie/ponytail holders in one drawer, hair clips in another, and head bands in another. If the drawer is too full - that means they have too much and time to get rid of it, lol. They are also in charge of keeping it clean and organized.