I keep my cannulas in their boxes and have a shelf for them. It depends how many you get at a time. I know some people are given months' worth, but I order as needed so get a couple of boxes at a time. Yes, sometimes they do take up space, especially when I have a new order arrive and old ones left. I used to keep one side of a cupboard for them. Basically, put them wherever you have room! You'll find somewhere that suits you. Also, think about where you'll be changing the sets. I use my bedroom so keep them there.
My back up pen I just keep downstairs near my bag ( as back up if I go out, etc) where it was when I was on MDI.