Wow. It sounds like you a really committed in your regular life–good for you. I try to eat organic and things like that but I have no patience for second-hand stores.
Anyway, on to your question:
1. Venure–We are getting married at an aquarium which has all sorts of feel-good benefits to it. A portion of our fee is a donation to the aquarium, they emphasize organic and sustainable food (in particular, sustainable fisheries), and they have composting and a rain collection system. They’ll also have interpreters there during cocktail hour to talk to anyone who’s interested about marine life.
2. Caterer–our caterer is included but our emphasis all along was on finding an organic caterer that specialized in local, seasonal ingredients. Or at the very least, a regular caterer would would do that for us.
3. Favors–don’t have them. No one takes them home and it is extremely wasteful. If you want to do something, make a donation to a charity that is important to you. (That said, we will have favors. I didn’t want to, but my mom wanted to make jam. It’s a very sweet gesture and it is cute. Plus it is huckleberry jam so it is something particular to our region.)
4. Stationery–I hope to find some great recycled stationery. I’ve also heard of people using paper from alternative materials (elephant dung, anyone?) but for our wedding, which is pretty formal, I don’t think we are likely to find anything that looks right.
5. Flowers–get whatever is local (this will also save you money). Also, consider only having personal flowers (bouquets, etc) and doing non-floral centerpieces.
6. Vendors–hire vendors that give back–either through donating their services or money. For example, our photographers give 1% of profit to the american breast cancer foundation. I’m also planning on going to a charity auction for brides-to-be and hope to get a lot of the vendors (or at least extras) that I am less picky about there.
Those are the main ones that I’ve thought about. Good luck.