1- 2 pairs, plus a bathing suit. Any shorts are appropriate as long as they can last the whole season. People were canoe tripping long before the development of new fabrics such as polyester and polypropylene, which have become popular among staff and veteran campers. Those who wear them praise their ability to stay warm when wet and wick moisture away from the skin on cold, rainy days. They also dry phenomenally fast.
Most people prefer to wear mid-weight long underwear.
Brands include Patagonia, Capilene, Helly Hercules, and REI, to name a few. Similar in material to the long underwear bottoms above. This item is not crucial but tends to make cool, wet days a lot more comfortable. Flannel or cotton shirts are quite suitable. They provide protection from the sun and insects and are comfortable when it is cold.