Dry clothes and a towel , sealed in a watertight plastic bag. If you tip over, you'll want to change. Food and water - canoe trips can last hours. Bring sandwiches and snacks in a cheap cooler, in case of a tipover. Alcohol has a dehydrating effect, and the combined effect of drinking, the hot sun and the work of paddling is stressful, which can wreck havoc on paddlers who are not in shape.
Heat stroke is a real danger, along with heart attacks and other unpleasantness.
Also, drunks are loud, obnoxious and boring to others seeking a peaceful experience. Wear shoes that can get wet such as Keds or windsurfing slip-ons, also known as riversiders, riverrunners or wading sandals. When taking a break, staying with your canoe will keep others from borrowing it. Your canoe can be flipped back over. Over-turned canoes float.