FlightofFancy, I worked up to 2 weeks before my due date first time round(though there were quite a few bank holidays and I took days off here and there so I only did a 4 day week in the last month or two and I did appreciate that as even though I was office based I was dreamy and definitely had less energy). Then I used holiday and actually planned my maternity leave to start 3 days after dd was due (that was when your leave had to start on a Monday) and she was born 2 days after that so worked out just fine. But, I was lucky, and had no pregnancy 'problems'.
Planning something similar this time, though I will be finishing on 22 December and not due until 24 Jan, because of Christmas... was going to be off from 22 Dec to first week of Jan anyway, and then would want to take 2 weeks before due date, and it just doesn't seem worth going in for 1 week after Christmas - can't imagine I'd have any motivation left at all anyway, and imagine I will be more tired this time round, as you just don't get time off in the same way once you've got a little one already (that's not meant in a 'you just wait' way to first timers, by the way, and I'm not jealous, I adore my dd and she's worth it).
If the baby arrives earlier than you planned your leave to start it will just kick in automatically on the day of the birth and you can reallocate your holiday - as long as you make sure you have an agreement that you can carry anything you are owed over into another holiday year, if your leave is going to span 2 holiday years.
Re buying stuff, I also bought almost nothing until the last minute - living in a city it is entirely possible to simply walk in a buy what you need (you just may not get the best deal as you might find in the internet). I walked into M&P the day after dd was due and walked out with a pram - needed the imminency to help my indecisiveness, and goodness, I got great customer service! (It was half an hour before closing time on a Saturday, and they said 'when are you due?' and all scrambled round me when I said 'yesterday'!).
I had bought the car seat a couple of weeks before, along with the crib, so that, as someone else said, if she were a little early we'd be ok. I had a chest of drawers delivered a week before she was due and had great fun doing flat pack assembly with a huge bump (managed it though!). I bought exactly no clothes, as my mum had already bought a pack of vests and a pack of babygros and I didn't see any point buying anything else beforehand.
TBH, if you live somewhere close to a decent dized mothercare, or M&P, or John Lewis then you'd have no problem sending your DH to the shops after you gave birth to get you a car seat and I'm sure he'd be back before they'd be ready to discharge you, even if you went for the minimum 6 hours in hospital..
So, if you don't fancy baby shopping yet, don't feel you have to do it.