I have a couple of racks of clothing and models always seem to enjoy rummaging through them and often end up with stuff that they really want to be photographed in.  However, I buy very little everyday wear (which a lot of models turn up with), so the collection is largely "party" stuff.

I have of modest supply of shoes and boots, but largely rely on the model to bring what fits them. Ditto for underwear.

I also have a large collection of costume jewellery - it is always well recevied.

I am very happy when a photographer provides wardrobe so long as it is clean and it fits me A few clips work when something is a little loose though!

I used to keep some basic items in case a model forgot wardrobe or brought crap.  Wouldn't just use it "just because" though, would have to be one of the aforementioned situations otherwise you'll shoot it so much you'll get tired of it.  No point in shooting the same dress 7 times for example.  Just keep some stuff for emergencies.