You don't really need to buy anything.
Just do some pushups, pull ups, run/jog a few miles or ride your bike 10 miles or so depending on how good of shape you are in.
Throw in some yoga stretches before you start.
If you have a couple dumbells aleady, you can do some curls or squats with those.
Another exercise is to go sailing (singlehanded) when it's blowing say 20 knots and above. Do lots of tacks and gybes and have too much sail up while you do it. That will give you a workout especially on a small boat
. Add in reefing in the middle of this sailing exercise if you reef/raise the main at the mast
. Then lower the mainsail
and re raise.