Seriously, the carrying capacity of a boat is one of the reasons that it is hard to do this trip in a boat that small. The amount of water that the average American uses in a few days would swamp a boat that size. Food, water, motor and cooking fuel, tools, spare parts... can quickly lower a small boat's waterline to where it's dangerously low in the water in rough conditions.
Another concern is the crew's ability to rough it while being bounced around in a boisterous ocean for a few weeks, and knowing their realistic limits and abilities. Another is knowing the crew's self-sufficiency, ability to improvise, ability to stay mentally focused and upbeat in an alien environment far far from help when things go wrong -- and things do go wrong unexpectedly at sea.