Picture this, you're riding over to the park to meet your friends for a BBQ (winter BBQs are one of the luxuries of living in California or the southern hemisphere) and you get a flat tire :(.

No problem.  You've got everything you need to fix a flat in your back pack... except you took your pump out of your bag to make room for all those burgers, buns, and beer you're haulin'.  Uh-oh.