Racks

If you decide to go with panniers, make sure to buy bombproof racks. When I walked into my local bike shop to buy my racks and panniers, I was given a strong recommendation to buy racks that were strong enough to support the load that I would be hauling. That seems pretty obvious - but you have to remember that there are a lot of racks out there that are inexpensive and can handle a light load but that will break under the pressure of a fully loaded tour.
The racks I chose for my fully loaded tours with panniers were from Bruce Gordon. These racks were made of chrome-moly with a minimalist but very strong design. Strong & light - that's what I like! I used a rear rack, and a low-riding front rack.

When I chose to use panniers to carry my food and fuel on a trip where my primary hauling mechanism was a trailer, I used a folding rack (folding bike, folding rack - I think there's a theme here!) from Bike Friday. Again, a chrome-moly rack, with a sweet design that accommodates folding to pack with the folding bike at the end of the trip.

There are other good racks out there too - just make sure that the racks you choose are rated for the load you intend to carry. When I met Mickey (a Transam rider) in Missoula on my first trip, he was on his 3rd rack. His rack kept breaking, and luckily the manufacturer always replaced the broken rack for free. That's great in that he had no additional cash outlay - but you can't guarantee that you'll be anywhere near a source for a new rack when your rack breaks. It's much better to start your trip with a rack that will hold together under a full load.

And remember, on some of your tours you're likely to be passing through some pretty empty areas. I've been on trips where I was days away from a bike shop (and the little ones in the middle of no where aren't likely to have the kind of racks that you need), and in places where overnight deliveries take at least two days.