: Do I need bulkheads in my kayak?

No.

: Are there reasons besides providing 3
: separate floatation compartments and adding some stiffness?

Yes. And all the reasons are very good. Ranging from foot braces, flotation, dry storage, safety, easy of use, and more.

: My kayak is 14
: ft, already very stiff, and I'd rather not put bulkheads in. For safety
: purposes I could always use flotation bags.

Yep, you can. Read up all over the net on the advantages of both and come to a personal conclusion. My own opinion is that I'd never leave home without them. In fact, at work we don't allow boats on the water with us unless they have dry storage areas and bulkheads.