If you own a higher-end road or mountain bike with a Shimano drivetrain, then chances are it's got a "secret" storage compartment: the hollow space in the axle, that connects the Shimano Hollowtech cranks. While you're not going to be able to fit your phone or wallet in there, you can pop in the new CrankPump CO2 tire pump.
To install the CrankPump, you just remove the crank's existing plastic end bolt, slide in the pump, then screw its own fiber-reinforced nylon bolt to secure it. An included foam insert keeps its CO2 canister from rattling around while you ride.
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When you get a flat, you unscrew the CrankPump and pull it out, then pull off its two TyreZip levers. These are used to essentially "unzip" the tire bead from the rim. Once the tube is patched (or the burped tubeless tire is reseated), you reinflate the tire by just pressing the business end of the CrankPump up to the valve stem. It works on both Schrader and Presta valves, and can inflate a 23-mm road tire to 90 PSI, or a 26 x 2-inch mountain bike tire to 30 PSI.
The CrankPump reportedly should fit inside most recent Dura Ace, Ultegra, XTR and XT crank axles, among others.
Its London-based designers are currently raising production funds, on Kickstarter. A pledge of £15 (about US$25) will get you one, when and if they're ready to go. Note, however, that the single-use 12-gram CO2 canister must be provided by the user, since such pressurized containers can't be shipped by air with the rest of the pump. They typically sell for less than a dollar each.
You can see a demo of the pump in the pitch video below.