I second the motion of using water for ballast. Wherever you paddle you will have plenty available. When you finish paddling you can empty your ballast and return it to its source.

At about 8 pounds to a gallon, 6 empty one-gallon milk jugs, or a dozen empty 2-liter soda bottles adds almost 50 pounds to your loaded weight when they get filled. And when they are empty they weigh nearly nothing. A light, and simple, wood rack can be assembled from scrap 1x2s to hold your ballast in place along the length of the keel

By dealing with your ballast in "chunks" of 4 or 8 pounds (the approximate weight of 2 liters or a gallon of water) you don't have any seriously heavy lifting to do if you handle just one bottle at a time. Should you find some souvenirs, catch a few trophy fish, rescue a fellow kayaker, or in some other way acquire more weight during the course of you trip, you can easily dump the water from your ballast.

And the empty bottles serve another purpose. Should you get a hole in the boat you can dump the water from them and use them for 50 pounds of additional bouyancy. Try turning 50 pounds of iron into 50 pounds of flotation!!

You can of course bring along a bottle or two of potable water, or some other beverage. And of course one of those empty bottles can serve a turn in the personal hygiene department should your kayak lack rest room facilities and a holding tank.

Just a few thoughts.

PGJ