Re: Don't read this unless you have time . .
Do not listen to everybody. The only thing you need before you leave the dock is a strong rig, VHF, Epirb, Harness and Jack lines, and a tub of this no-seal stuff that you can shove in any hole that make be caused to occur in your boat to stop water intrusion immediately. Seriously you can take a glob of this stuff, shove it in a 2 1/2" diameter hole with water spouting in, and it will seal and stop it in seconds.
Oh and you should probably have some charts of where you are sailing- So I think a handheld GPS is important as well. And a life vest. And some sort of auxiliary power source in case you lose or have no wind so that you can keep control of the boat. And an anchor in case all else fails so you can have time to get a solution worked up and avoid a worsening situation.
That is all you need. The rest is just conjecture.