front will be fine with 20 lbs on back. Keep the tire pressures at the max or close to them, this will help a lot avoiding getting flats, not to mention make it easier pushing along more weight. Soft ground is soft ground, the bike will be heavier than usual so you have to use common sense.

rear panniers are very handy, even just for keeping stuff in one place, drier even if not waterproof as you can use garbage bags to pack clothes etc. If you have a rack already, why not borrow panniers if possible (if you dont have them already)

you will get lots of advice, but seeing if all the bolts etc are tight on your bike before going, wheels are in good shape (perhaps have a bike mechanic check the spokes) and tires in good shape--all this is a good common sense thing to do so that you dont have probs. Not heavlily loaded and a bike in good shape, it should be fine.

*making sure you have adequate water is a big one, I second or third that. it sucks to be hungry and especially thirsty.

have fun