Depending on what type of boating you plan to do, there is a wide variety rescue tools that may prove useful:

• Sling or Guide Belt
• Throw Ropes
• Messenger Line
• Pin Kit NOTE: We cover pin kits in much more detail in the SWR Class and show you how to make better and cheaper versions than the NRS Un-Pin Kit
• Folding Camping Saw (Stainless Stell Blade)

Theres always a trade-off between weight, space, etc with small craft like kayaks that you need to consider.  Canoes and Rafts don't have these same limitations but when they get stuck, its a far more serious matter.