Thanks, Perna...I know it's not much, but it's the principle, dammit!
Thing is, it could be my flatmates' friends for all I know...some of them seem to spend more time here than I do! A food locker might work, but I can't help thinking that doing something that stands out might just encourage them.

Anyway, everything that's gone so far is easily replaced...it'd just be nice if I didn't have to. One of my flatmates said someone had used her milk as well, so I'm not the only one.