Sometimes (rarely, for me at least) you can see where the tire was punctured by seeing the culprit - glass, nail, etc - and then pull the tube out as he suggested and patch there. And yea - to reinflate you do need a pump, but i always carry one on rides.

Any suggestions for good patch kits? I'm using one of the "vulcanizing liquid" kind, and I'm not wild about it. It's okay, but cumbersome.