I no longer use the commercially sold vacuum bags that you roll up to disperse the extra air. I couldn't control the size or relative flatness of the end product. (Maybe I was overloading them?)

Anyway, I do use gallon- and quart-size ziploc brand bags on all my trips. They really keep me organized and everything stays dry.

My variation: I make sure that I have a drinking straw with me to get the air out of the bags easily. (You'd be surprised how much air you can suck out of a seemingly compressed bag that you've already "pressed" the air out of.)

Thanks for the reminder about the availability of 2-gallon ziplocs. Will stock up!!