The Small Vessel Regulations enforced by the Transport Canada establishes a minimum of safety equipment that you must carry with you in your kayak (or any vessel under 6 meters in length): 

1. Personal flotation device (PFD). When selecting your PFD you’ll want to make sure that it is certified by Transport Canada that it is designed specifically for paddling, and that it is [preferably] equipped with some kind of reflective device.
   
2. Throw bag. You must have a throw bag with at least 55 feet (15 meters) floating line. In an emergency situation it can literally be a lifeline between you and your paddling partners. The floating rope can also function as a tow-line between kayaks and around camp it can serve as an excellent way to hang clothes up to dry. 
   
3. Bilge pump or bailing scoop. For emptying water from your kayak while paddling, nothing beats the efficiency and ease of a hand pump (especially double action models). If you don’t have a pump, a bailing cup or scoop is required to help get rid of excess water. The addition of a sponge lets yousoak up the last remaining drops of water, keeping your kayak warm and dry.
   
4. Signals. You are required to have an easily accessible sound signaling device, such as a whistle or horn to alert larger watercraft to your presence in low visibility conditions. 
   Signal/running light. Between sunset and sunrise, or during times of reduced visibility such as fog, you must remain visible with the use of a running light (or at least a waterproof flashlight).
5. Spare paddle (optional). Usually a 2 or 4 piece 'break-apart' design, every group should carry one. Oftentimes it can be secured on the deck of your kayak via shock-cord deck rigging, easily accessed in case of an emergency.
   

For mandatory equipment see the Transport Canada.