Same as Christy......I had 3 overnight sized bags (for all 3 births).

*One for me and my stuff for the stay in hospital
*One for baby and all their stuff
*One for actual labour....(including CD machine and oil burner, big towel, special t-shirt, snacks for DH etc etc)

Don't stress over how much: always best to have too much than not enough......I was embarassed at how much I had at first with Olivia's birth, but realised that everyone is so focused on you and your baby, they don't care about your luggage!!