I regret not eating more than a couple of bites of any of the food we'd so lovingly chosen, a friend who runs a cafe had gone all out and put on a lunch that was served at the table (quiches, tarts, salad, cold meats, whole salmons...) but I couldn't eat a bite! Ditto the mexican street food that arrived in the evening.
Regret not making my sister my chief bridesmaid, she is my best friend. The girl I since chose to be my CB has gone NC 
Also, be nice to your bridesmaids! My gaggle of girls had never really been involved in weddings and didn't know what was really expected of them and I wasn't very nice about this the day before when I was at breaking point trying to get the hall set up. The most important thing was that they were there and celebrating with me, in the end.
Don't let your photographer leave early! Mine left before a big surprise my mum had planned for me and would have loved professional photos of the looks on everyones faces.
I DON'T regret: making my own dress and most of the decorations, doing an impromptu speech, not having a standard 3 course roast dinner thing, wedding cake as pudding, pretty much not leaving the dance floor after the first dance, not having posh cars or favours, wearing converse instead of shoes I couldn't walk in, wearing pretty much my own every day make up (it is a myth that you need loads of slap for good photos!) and of course... I don't regret marrying my DH!