Buoyancy aids for canoeing and kayaking are an essential piece of kit and you shouldn't paddle without one. These are also know as Personal Flotation Devices (PFD).
Unlike lifejackets, buoyancy aids are designed to assist with your flotation whist still giving you freedom of movement for paddling and swimming in.
Buoyancy aids differ slightly depending on the type of paddling you take part in. For example, touring and sea kayaking buoyancy aids tend to have more pockets and white water ones will have more rescue attachments available.