If you enjoy long bike rides, it's really a good idea to keep some kind of repair kit with you at all times. A good kit will include the tools necessary to repair, at the very least, a flat tire. You may also want a kit that will help you repair a damaged wheel or chain.
The type of repair kit that's best for you will vary depending on the bicycle you ride, how far from civilization you tend to travel and the amount of work that you're prepared to do on your own. Repair kits range from simple, five dollar tube repair kits to elaborate assortments of tools intended to help you fix nearly any kind of mechanical problem.
Some questions to ask yourself while shopping for a repair kit: How often do I ride my bike? How likely am I to end up stranded somewhere with suddenly non-functioning transportation? How fancy is my bike - will it need a lot of maintenance or virtually none? How expensive is my bike/do I want to spend more on the repair kit than I did on the bike?
Any good biking store should carry a few different repair kids. And you know where to check if you need a good bike lock - the bike lock specialists at A & J.