Do you ever get a flat tire while you're in a bike shop, right there with all your tools? No! You get flat tires on the road, just off the highway near the intersection of "Middle of Nowhere" and "Most Inconvenient Place to Get a Flat".
I got this flat in Lynnfield, MA, seven miles from the nearest bike shop, while biking to Montreal from Boston. Seven miles is a long walk!
What did I learn?
1) check the tire before you go to a bike store. If it's just a puncture, patch it.
2) carry a patch kit.
3) if the problem is worse, take the tire off the bike and take it to the bike store with you
4) quick-release bike tires. Always.
5) it's awesome to know how to replace a bike tire without tire irons! Don't waste money on tire irons!
6) better than going to the bike store: carry a spare tube!
Do most people carry bike tools? The answer to that is also no!
Here's why you don't have to!
Step 3: The Tubes!
Check this out - Rite Aid sells both bike tubes and wrenches. SO CONVENIENT!
Step 4: Tire ON, no tire irons
Use your thumbs to press the edge of the tire up over the rim.
Work towards your chest, at first. When you're almost done, turn the tire so you can push away from you.
Do one side first, then flip the tire and do the other.
At the very end of the second side, it'll get a bit tough, but if you press through and really apply effort, it'll pop on.