If you want to bring your sail along for later use, there are two ways to transport it: 1) furled but mounted in the mast receiver, or 2) horizontally along the starboard gunwale (port side interferes with the rudder control).
To make it quick and easy, I keep the sail unsheeted until ready to use. I use a small snaphook (a carabiner might work just as well) for quickly sheeting the main when ready. While detached, I substitute a small "tail" (see below) to keep the sail furled (the knot slips around the furling hook). This comes off
when you sheet the sail.
To secure the mast/sail horizontally, I use a loop line mounted to the forward hatch bungee (adapted from Stobbo
's loop bungee) to contain the mast foot, and a small line (not shown) to secure the sail amidship. This keeps the sail up and out of the water but doesn't crowd you in your seat.
close-up of loopline
The one thing to remember if you transport the sail unsheeted is to pre-rig your mainsheet so it's ready to attach to the clew! Above all, stow it with the sail or in one of the hatches so it doesn't get left behind!
It's not too difficult to step and dismount the sail at sea, but a little practice builds confidence. It's also possible to fetch (and rig) the mainsheet from the aft hatch if you forgot to pre-position it, as long as you're not in a hurry! Best to practice it just in case.
Advantages: stowing vertically makes you more visible (you can even add reflector tape if this is a concern); stowing horizontally keeps the mast from bouncing around in the mast receiver (and acting like a pendulum in heavier seas) and offers less wind resistance, especially upwind. I prefer horizontal -- think it is easier on the hull.