A few things I have experienced at previous weddings that have been less than ideal:
A church wedding, where the church had no toilet, and there were over an hour of photographs after the ceremony, which had already taken an hour or so, and a journey there, which was also over an hour, followed by a 45 minute drive to the reception venue. This meant that it was nearly 4 hours after gulping my morning coffee on the way out the door till I could wee it out again. Not good!
Whilst the bride and groom can't control the weather, they can control how long photos take, within reason, and I get that they want the special day captured. But having guests waiting around for 2 hours when the weather is indeed shit, and your outfit doesn't take it into account (and this can be hard in July, when it should be warmish, but is more like 9 degrees) is wrong, and if this is to happen it should at least be that there is somewhere indoors they can wait. Preferably with booze and canapes, but this particular day I nearly went and sat in the car I was that cold.
If someone could magically make it that high heels don't sink into grass that would be fab. I get that this is a big ask 
I dont mind whether people ask for money, have a gift list or wishing well or whatever, that's personal preference and doesn't affect me.
People saying about having 4 bridesmaids - I was actually guilty of this, but is sort of "just happened". Basically I wanted my 2 close friends that I'd been sharing a house with for the past 3 years on the lead up to my wedding, and I thought that would be it. But I went home for a few months (abroad) after my visa ran out while I was awaiting further entry clearance and got back in touch with my absolute best friend from high school who was moving to the UK and would be in the UK for my wedding, so naturally I asked her to be my maid of honour. Then, once I was back in the UK my sister in law asked me if her daughter could be a bridesmaid, IN FRONT OF HER DAUGHTER, who would become my niece. Mother in law was also in the room, and her mother, and I really didn't feel I could say no. I realise I could have, but for the sake of family relations I said yes. Hence I ended up with 4 bridesmaids! Which is no big deal, the money wasn't a problem (Bridesmaids can be expensive). It was just one of those things.
That said I went to a wedding where the 3 year old son was the "best man". Churlish of me as this is, I thought that was really naff
for reasons I can't understand or control
so we all have our little bugbears.