While paddling the Big Bend and the Everglades in particular, opportunities to resupply fresh water are limited. In the Everglades, you will not be able to resupply water between Everglades City and Flamingo. This means you have to carry at least a week’s worth of water (7 gallons) and ration one gallon per day. To carry all this water, use 2-3 large backpacking-style water bladders. I used the MSR bags pictured here.
The benefits of using these bladders is that once empty, the bags fold up and take hardly any space, unlike a bulky hard-sided container. Racoons however, will chew through a bladder to reach the fresh water, and so all bladders must be stored inside your kayak overnight.
Experienced backpackers might be tempted to bring a water filtration or treatment system in order to drink water from rivers. Do not do this. A consequence of the topography of Florida is that every creek and river is polluted with agricultural run-off (fertilizers and pesticides). No field treatment system can make this water safe to drink. Thru-paddlers are limited to man-made sources of fresh water, so careful planning and attention to supply locations on maps is necessary.