The point is to be warmed up before you enter the water. To "acclimatize" yourself with the surrounding environment (the cold, that is) before sailing out, isn't good. Neither by approaching the surf spot with the car windows open, nor rigging your equipment in your fancy summer dress. The heat fan of the car shall be working hard during your drive, and the dress during the rigging process have to be adjusted to the cold environment (especially the cap is important).

As it's almost impossible to avoid getting cold fingers during the rigging process it's a good idea doing some gym just before launch. It's not exactly smart to enter the water with cold fingers!

A very important precaution is to consume a lot of liquid before getting on the water. Dehydration is a very efficient shortcut to tiredness (cramps), hands, fingers and feet perished with cold and hypothermia (general frostbite). 

As to drinking, we're absolutely not talking about alcoholic drinking here. Perhaps alcohol for a short period of time pleases you with a comfortable warm feeling - but this feeling is just a symptom that warm blood leaves the core of your body and is pumped out in your cold limbs. And when the the now cooled down blood returns to the core of your body (your heart), you'll have to use a lot of energy to re-warm the blood again. To connect winter-windsurfing with alcohol is an invitation for hypothermia.

Lastly: Don't let the fear from peeing while on the water urge you not to drink plenty of liquid before launch. All serious winter-windsurfers pee while in their suits - and frankly they enjoy!