Jonathan,
Are you going to a Rick White Sailing Seminar? Sounds like it. If so, you will rarely be on the water for more than about two and a half hours at a time (a morning session and an afternoon session).

And even if it is some other seminar that I have never heard of, no clinic of any kind would keep you on the water for eight consecutive hours. That would not be conducive to learning anything.

So whatever you normally take with you when you go out for a two-hour sail would be what you would take when you do the seminar.

I recommend good body protection, though. You should wear wetsuits and, if you do not have reinforced knees on them, wear knee pads on top of the wetsuits. Also, good sailing gloves, of course. And you will be working harder at sailing than you normally do when you are just out there sailing around for pleasure, so do take more water than you usually do. If possible, store water in the hulls -- you don't want a cooler or anything cluttering up your deck. In fact, you do not want anything extra that lines can get caught on. During the drills, you will be doing a lot of tacking and jibing, and you need the deck to be as "clean" as possible.

If you have other questions about the seminar and what you need to prepare for it, whether it is ours or someone else's, please e-mail me.