My wife is picking up some baby bottles for me today to store washed yeast. I know it sounds weird, but here are a couple benefits.
1. They are good size. She is getting 8 ouncers
2. They are easy to sanitize. You can microwave them in some special bag and they are good to go.
3. The number one nipple serves as a good air lock. Obviously you have to also cap the nipple, but it's enough clearance to allow the escape of CO2 without allowing a ton of room.
4. Easy storage.
5. Cheap, they like $1/bottle.
1. They are clear, so you'll need to store in a lunch bag or something.
2. The airlock isn't 100% against allowing airflow in the other direction.
At least these are what I have found to be true.