We decided a week before ours that, so long as we actually managed to get married, we'd cope with whatever shit happened on the day.
Our driver got lost in the way from the church to the reception, which led to us being quite late. And my FIL decided he didn't like our seating plan and wanted to mix it up a bit. We directed the driver back to the Embankment, and my parents simply intervened calmly to say that since we had chosen that plan, there had to be a reason, and put everything back as it was intended to be.
Oh, and we realised in the Thursday that the thing we'd forgotten that was most crucial was to buy a wedding ring. I spent my lunch break racing round trying to find one that would fit my chubby fingers and settled on a plain silver band for £12. I still wear it :)
The only thing that could have been a disaster was that my suitcase didn't get taken to the hotel for the wedding night, and I'd have had to go down to breakfast in my wedding dress if I hadn't been able to borrow some trousers from SIL.
So: make sure the driver has a map if needed instead of assuming they'd look up the route in advance, make sure nobody fucks with the seating plan, double check you have wedding rings, and make damn sure your suitcase gets to the hotel for the wedding night. And realise none of this would stop you actually getting married, which is what really matters in the day.