1) If you buy beer, try to buy it all the same type (ie. all brown glass bottles, or all green glass, or all aluminum, whatever your preference is). That way when it is time for you or a camp mate to bring me the bags of recycling, you won't have to separate a lot, just minimally.

2) Try to bring as many re-usable cups, dishes and silverware as possible, even to share, I hate red cups more and more (although at my parties I soak and rewash most of them, AND they ARE curb recyclable, so they aren't all that bad IF you must)

3) Remove as much wrapping from food products as you safely can BEFORE packing, it will minimize the amount of trash left for someone to clean up and haul out.
(Examples: remove plastic from juice boxes *smirk*, remove inner bread wrapping if double wrapped, remove the wire ties from veggies such as spinach, remove tuna fish and any other can labels and write with permanent marker what it is (I know you think I'm crazy by now)

4) Place food that needs to be kept cold in plastic containers with lids. It keeps the food from being tossed around the cooler and eventually going into the trash because it got soggy or meat juice all over it.

5) Put your eggs in an egg container, they are $2.99 at Target and will keep your eggs from breaking and minimize the trash at the event).
I hate it when my cheese is all wet because I used a ziplock bag instead of a hard plastic container and my milk carton falls apart when I pick it up because I bought the cardboard kind and not the plastic kind (btw, you can recycle the cardboard milk, but the plastic milk jugs can be recycled for $)

6) Use a mesh laundry bag for your wet trash instead of plastic garbage bags, it will let it all dry out and not stink or leak in your car when you haul it out.

more to come

any other ideas?