Usually I wear a Boss suit, looks good in everyone else photos or whatever will fit into the day, The amount of times a second shooter turns up in a check shirt and baggy trousers for me is once, as they will get into some shots and really look out of place, not good as far as I'm concerned. The moneymaker and bowery are part of that smart look too, plus they feel great and start conversation most weddings, apparently I look like Bruce Willis. Although that was said when I was just in a white T-shirt and jeans in an ice cave, I kinda understood that one. For shoes I wear Clarks, they are very comfortable all day [tested over 14 hours, sadly] and have a clean/smart look. I think making the little extra effort helps on the day but you don't have to go over the top & I'd rather fit in to the crowds dress sense as I am part of the wedding standing right beside the bride/groom of a good part of the day, you are going to get in photos that get shared from time to time.
The good shoes really was the best investment I ever made, if I have a long drive home a fresh pair of socks and some trainers for the drive = bliss.
In the bowery I usually carry two extra lenses a flash+cable [perhaps until good triggers are available] batteries, cleaning cloth, SD cards, business cards etc... Everything else is in the rollers until I know need it. That's for the working part of the day, the 'church' and the procession into the reception, the formals are a one camera affair, more or less. The afters also one camera only.
I eat nuts as well as oat bars and always have some water near by, eating a banana each day for the week before a wedding will help with the cramps - that and doing weddings regularly, ha!
Hope you had fun, I really like weddings, so personal to be invited to stand right next to a couple while they tie the knot.