well I had my bag packed from 37 weeks and by 42 weeks I was taken in to be induced so off i went with my bag.
I was in hospital for 3 days before baby arrived and in that time I had to send out for more underwear and clothes. It may be best to have an extra suitcase for yourself tucked in car, just in case.
Also if you go in for induction, books and magazines come in handy and plenty of money for phone and TV as the days do drag if you are waiting.
I took some snacks for energy and had some lucozade too.
If you are taking a tens machine, make sure you have spare batteries too.
Disposable pants are very uncomfortable Id suggest getting a big pack of cheap underwear instead and lots of pads, Maternity ones feel like bricks but are the best for first few days after birth.
I have since been told that arnica tablets help with bruising so perhaps think of packing some for after the birth.
As for baby, take babygros, vests and hats and a nice going home outfit plus the usual nappies and bottle / milk if you are not breastfeeding.
cant think of anything else as yet but will pop back if i do.
best wishes for the birth.