I always carry 2 tubes and 5 one dollar bills.. The dollar bills can be used as an emergency tire boot or for bus fare..

Pinch flats are common. Should be 2 small punctures that look like a snake bite or perhaps you had something penetrate the tire just enough to puncture the tube but not stick / stay in the tire..

Also, check the tire carefully.. I've had several instances where I thought the tire was clear of debris only to get another flat. Closer inspection reveled the culprit still in the tire but it would only protrude under pressure causing it to penetrate the tube..