When cycling in the countryside, you should always carry a spare inner tube with you, not for your average puncture, which you can easily repair, but in case the whole inner tube gets ripped. A simple puncture will give you a chance for a nice break in the shade under a tree while you fix it. Carry a few tools and puncture repair kit, and take a break.
Always carry a puncture repair kit, which should include a small piece of sandpaper, some vulcanising patches and some glue. You will also need a pump and two tire irons.
Identifying the Hole
Push the valve into the hole in the rim so you can't see it sticking out anymore. Pull the tube out and away from the wheel, and fill it with some air. Hold the tube to your ear and listen very carefully for the sound of air escaping. After you've identified the hole, roughen it a bit with the sandpaper. Apply a thin layer of vulcanising solution to an area larger than the patch you plan to use and allow it to dry.