I didn't pack my clothes until the day before I went into labour (and Nat was a week o/d). I didn't have enough clothes to do that. So I waited until I felt niggles, then packed Other things like pads and undies and spare toiletries I packed in advance, just gradually stocked up on things when doing the shopping in the weeks leading up to it.
Ooooh, how exciting for you to be planning all this!