Something else you can do if you're going out to a beer bar or something is tuck a fresh ziplock baggie in your pocket.
It starts out sealed and sterile on the inside, and it's much easier to carry than an empty, recapped bottle if you decide you want to save yeast from something that you're drinking. I just toss it in the fridge when I get home and pitch it from there into either a beer or a starter.
"I can't believe how many people think Air Lock is pronounced Hydrometer." -BigKahuna
"If you gave me a beer with placenta in it without telling me I would kick you in the nuts." -ODaniel
"We be in a big hurry for dope beer with much alcamahol and flavor, quality, balance, and aroma don't matter. We just wantz to be druck, u know?" -Yooper