Take a look at Louise's Reno pages
and her recycling page at
I would suggest not shopping in San Francisco and then hauling all your supplies up the Sierra Nevada Mountains into Reno. Goods in Reno are probably cheaper than in San Francisco, and you won't have to buy extra gas to haul the heavy load.
Making charitable donations of gear used on the Playa might not be workable, as cleaning the stuff will be very expensive for the charity.
Instead of renting a car and buying food and gear, you might consider using the Green Tortoise bus, which operates in conjunction with a hostel in San Francsico. I can't connect to the site at the moment, but try this URL for more information:
My recollection is that you get a group to camp with, transportation to and from the event (San Francisco-based), all meals, and they _may_ supply tent and bags, but check that on their site. You'll need to find their Burning Man specific page for information on what they supply and what they cost.
Additionally, Twin City Surplus has a program for out-of-town Burners; they will supply you with all your camping needs except food. You get all your gear, including water containers which you can fill at their store for $12. You can get your gear more cheaply by shopping around, but if you aren't familiar with the area, it may be more convenient to pay something extra for the convenience of driving up to one store and having all your camping supplies sitting there waiting for you. You'll then need to buy food, ice, and ice chests.
Some years they have a special page for Burners. Their current page for Burners just lists tons of items, many of which are useless. Drop them an email and ask what they recommend for you in your situation.
There are alternatives to renting a car, but it that's part of your longer term plan, go for it. You'll know best what suits your needs. Be aware that the car will be seriously filthy after a week on the playa. (Heck, it'll be seriously filthy after a day.) If you plan on using it for a month after, I'd give it some reconsideration. You'll not only have playa powder all over the interior, you'll have it in all the air vents. Every time you turn on the air or heater, you'll get a blast of dust coming out of all the vents. With the right mind set, that's sometimes a pleasure, but not if you're going somewhere in nice clothes.
Good luck and have fun.