Due to some communication problems I only found out today (thursday) that i was invited to a weddding reception on saturday, and i don't know what to buy as a gift.
I know this person from work, we're not the best of pals, but we get on well. I don't know his bride to be.
If in doubt, a bottle of Champagne I say!
You don't need to go for a hugly expensive one, it's just a jesture after all (well you do have the excuse you didn't have time to shop!), and I'm sure it will be thouroughly enjoyed when the couple get a minute to relax.
If you do want to spend a bit more then a couple of champagne flutes to go with it.