As a daytripper, I don't carry a lot in my kayak--just the things I need for the day, in addition to a change of clothes, safety stuff, etc. So, there is a lot of empty volume left over in the bow and stern compartments. I've always been keen on having additional flotation in my boats; thus I filled up large volumes of my wooden CLC Patuxent with closed-cell styrofoam when I built it. For my Epic 16X, I've found that empty plastic Tidy Cats cat litter containers fill up unused bow and stern volumes nicely, and weigh practically nothing. They come in various sizes, so one can somewhat customize how you fill up your boat.

A couple of questions: What is the difference in closed-cell styrofoam and any other styrofoam. And on your Epic, aren't the compartments already sealed floatation chambers? Just wondering.

In closed-cell styrofoam (and other plastic foams), each air cell is discrete and not connected with any other cell. In open-cell styrofoam (and other plastic foams), the air cells interconnect, like a bath sponge. Clearly, closed-cell is better for flotation purposes. My Epic's compartments are like any other standard hardshell kayak's; it's just that adding additional flotation within adds another layer of safety in case the hull is holed or develops some other leak. It is often suggested that kayakers add additional flotation to their boats via airbags (NRS sells these) or air-filled gear bags, if going on a trip. Belt AND suspenders!