Comfortable workout clothing is best, however, baggy clothes, such as long shirts and jackets or baggy pants and shorts should be avoided, because they can get caught in the wheels under the seat. The best rowing clothes are tight fitting, such as running tights or bike shorts. Wear layers so that you can remove clothes as you heat up. Synthetic, wicking materials are most comfortable for the bottom layer next to your skin. Gym shoes are ok early on when you are on land or on the barge. After that, you'll just need socks, as there are shoes mounted in the racing shells. Shoes that slip off easily work best.
Rowing is a water sport & sometimes you get wet, so be prepared. Toss a towel, extra socks and warm sweatshirt into your car or backpack. You might want a warm hat. Thin gloves are ok on the rowing machines, but are generally not worn on the water (it's a rower thing). Bring a bottle of water and wear sunscreen, even in cool weather.
Class will meet rain or shine (or snow) -- if it's miserable the class will work on the rowing machines inside the boathouse.