Something that takes a surprising amount of storage space is underwear, especially when you factor in socks. The ideal place for keeping it all is a drawer, or small chest thereof, but drawers are in short supply in a back cabin - I have just the knife/crumb drawer, and the big drawer under the bed, which isn't very accessible as I leave the bed made up when not travelling. My undies were in a box, taking up valuable cupboard space, but it occurred to me that there is a 'dead' space at the end of the bed, underneath the cupboard, where I could hang bags to keep my smalls in.
I was thinking I would have to make the bags myself, but then came across these (rather large for their intended purpose) peg bags, at £1.65 each in Wilkinsons. Already equipped with a hanger, all they need is a single hook to be suspended from, and are an excellent size for storing all sorts of things in all sorts of places - nice cheery pattern too.