On a night out I will keep my belongings to a complete minimum. My bag of choice will nine times out of ten be a clutch, so space is limited in any case. My current favourite bag is this faux leather clutch with a suedette panel through the middle - it's light, small enough to carry without causing a nuisance and allows me to carry the necessary makeup and night out essentials.
Obviously I take my ID (Still on my green card, hopefully I'll get a pink this year!), I usually take my student card for discounted entry and then keys and my bank card or money... for obvious reasons. Onto the good stuff.
I typically try to carry as little make up as possible just in case I lose my bag or something but there are a few bit I always carry. I never go out without my liquid eye liner - L'Oreal Super Liner- just in case. I rarely need it, in fact I never really do but since it's such an integral part of any make up look I carry it. Along those lines I always carry the lipstick I'm wearing that night. The last one I took out with me was the Maybelline Color Sensational in Hot Plum. Such a beautiful shade and it wears really well considering it doesn't dry out my lips at all!