Rough it for a few days. Don't bring a huge pile of crap to go camping. You'll waste a lot of energy hauling a lot of stuff.
Lose your windshield and mirrors. Look at the daily mileages you'll be doing. The normal GS rider thinks he has to have the bike COMPLETELY full of gas, you don't need that much gas with you. That's the easiest way to lose weight on the big girl.
Start running and doing some exercises, like picking up your bike. If you're in shape, you'll be much better off.
Equipment on the bike isn't going to make much difference. I found that the Kenda Big Block tires hooked up much better in the dirt than the TKC, along with having a stiffer sidewall for running lower tire pressures.