What you should bring for the two-day course
Extra change of warm clothes (preferably wool) for upper and lower body and feet. A thin fleece will be nice early in the season and on windy days. Food and drinks both days (preferably both cold and hot drinks). NB remember a cup for the tea/coffee!
A small drybag or bag to put stuff in on the trip on day two.
You should wear under the drysuit.
Warm wool with long arms and legs, and warm socks. You get a little wet around the neck and sleeves, but is mostly hot and dry.