I sailed the lower Mississippi Dec '09 (mile 600 to 304) and I can tell you it is quite a trip. The river is fast... seriously fast, to anchor for the night I would find an island and drift past it then motor upstream behind it to be out of the passing barge wakes, the only tricky thing is to make certain that you will not be land locked in the morning, the islands change shape. I would spot the desired island about 2 miles ahead of time and scope
it out as I approached, met some odd characters out there camping on the islands.
There is fog
, thick crappy fog
there are logs
, lots of them, try not to rip your rudder
any time anything goes wrong there WILL be a barge train bearing down on you, the barges are limited to 7 wide and 8 long but will often tie up together and be 14 wide, some throw 2' wakes, some throw 10' wakes, what is fun is when the wakes converge bouncing off the bottom and sides and make a big top hat in the middle..... wheeee....
the wind flows upstream, never mind what NOAA says the wind will be in your face. There were a few days that I had a north wind following me, I was able to make 130m in one day.
for fuel contact a barge and they will instruct you which are the re-fueling vessels, you can pull up and tie up to a re-fueling barge and buy fuel
Greenville "Yacht" club in Greenville MS has fuel, but the temperament of the marina owner had to be dealt with, and the docks are lined with old tire "fenders"
the Mississippi is a grand river and a force to be dealt with, I took out at mile 304 and took the Atachafalaya River to Morgan
City, the traffic was too heavy for my little boat.