Spirit Boat is such an amorphous concept that it can be either everything or only one thing (a physical representation). I mean, just about everything is a carrier or vessel - light, trees, water, envelopes - this could go on forever. What I prefer to do is focus on one thing and see how I can be creative with that one thing every day. It's difficult to see the variations when everything is a variation. Kind of like in a scientific experiment where you vary one thing and see how that changes the results. Two many changes and you have no idea what actually affected the outcome.
Now that I think of it, I believe Noah Scalin recommends choosing an object. He chose skulls and he's generated an endless supply of them with no end in sight!