I usually use a pair of rear panniers and a handlebar bag for a week-long tour. Yes, the bike handling is a little better with the load spread out to use front panniers as well, but for me it isn't worth the extra fuss and weight of a second rack and extra bags. I find that bags of about 2300 cu. in. will let me pack the sleeping bag/pad and tent inside with the rest of my stuff and leave the top of the rack open for any temporary purchases along the way. Currently using Nashbar's waterproof rear panniers - very basic with only one compartment each, but price effective.