I brought two of my cameras along to a friend's wedding once. One was a Kodak Brownie Hawkeye, loaded up with 120 film on it's 620 spools. The other was my 1965 Canon Pellix QL 35mm. I had a 50mm and a 135mm lens for the Canon. I'm not sure what the brownie is, but fairly wide.. with a fixed shutter speed of 100, and an aperture of whatever the heck it is.
I also brought along 1/2 dozen "disposable" cameras that I grabbed from the recycle bins at the photolab I worked in, and filled with fresh batteries, and Ilford HP5 film.
I shot with my own cameras. I think 2 rolls of Kodak Tri-X 120 (so 24 exposures at 6x6cm) and 6 rolls of bulk-loaded Ilford Delta 400.. so 34-38 per roll so a bit over 210, maybe as many as 220 35mm shots there.
The disposable cameras I handed off to other people, mainly kids. Out of the rolls from the disposable, I probably got 30-40 usable shots. Out of the 240+ I shot between the other two cameras, I probably ended up with another 10 120's, and 60-70 35mm shots.
All-in-all, 120-ish decent shots to include in the album I gave them.
It was all black & white.
I processed all the film & made contact sheets right away, but it was 9 years before I got them finished work on CD and prints. (I gave it to them on their 9th anniversary.)
They were floored. It was a lot more photos, and better quality photos, than they got from the photographer they paid. (Their words)
So.. don't go thinking you won't do a good job!
If you can recruit a little help with disposables, it's not a bad idea...and if you get COLOR ones.. you can have them developed & scanned to disk etc.. easily enough.
Look for things that will make memories of the day.. not ALL people, but they're the most important thing. If you can get the cake, any really nice outfits etc.., that's great too. It's a day full of candids.. a bit like street photography for much of it. Because you're "the" photographer.. you should probably pose them for a few important shots. Do so before they get wasted at the reception.
If you're having fun doing the photography, it'll probably come through in the work... so enjoy! Don't get messed up yourself until you stop shooting.