It's slang. It pretty much refers to the type which refuse to part with anything and everything on the off chance that whatever they're keeping will become useful to them one day. I believe it can be referred to as a medical condition, though it's more on the basis of attention seekers and obsessive compulsives.

[A smile!]

Anyway, I managed to get some help with our little thing. I need a favour in return. Do you mind?