Nail polish: Out and about and I get a call. Be to a casting in 30 minutes and it is for your hands. Oh shit! I don't have a manicure and my nails look like shit. Usually in a moment of panic like this I go for a quick 10 dollar manicure. Usually you can find one quickly, but if not you can also run to Duane Reade and grab a make-your-self a manicure-set for like 5 bucks.
Creams: A week is nice to prepare for a job that involves your legs but for a quick fix, use a cream that has a tanner or shine to it. Or use a dab, and just a dab of baby oil on your legs. It is good to carry cream on you anyways always!
Tampons: I have been caught way too many times without one, so I suggest from my own personal experience always, always carry a tampon on you.
Full piece bathingsuit and leotard, I am not even a full blown dancer or anything but I think having a bodysuit or a bathing suit or a leotard is an unexpected but needed piece of clothing for castings, especially for body.
I have had to buy shavers, tweezers, nail files, panty hose, underwear, along with mascara, during my running around the city to castings and modeling jobs.