I like the concept of a collapsible surfboard. If you could get the size down to a size that it might fit in a backpack (albeit a large backpack) you are on to something. This collapsible surfboard is just in concept stages for now. It is constructed from carbon-fiber which ought to make it light but expensive. It has hot-swappable fins and looks very slick.

It looks like everything fits flush, so there should not be too much extra drag from the joins. The only major drawback I would see is the possibility of breakage in heavy surf. Joins would be structural weaknesses and if the surf is pounding, there is a lot of force involved. For the vast majority of surfing conditions, however, this should be acceptable.

Yanko Design