I went looking for Gerber breast milk bags and found both Gerber and a brand called Lansinoh. See enclosed photo. I ended up buying the Lansinoh breast milk bags as they had a double zipper and the box said "the thickest bag available".

I don't have any experience with the Gerber bags. However, the Lansinoh also have a built-in pour spout.

So...does anyone make larger bags? ...or all they all 6oz?

Thanks for the tip! Here's a few more brand choices to consider:

http://www.nextag.com/breast-milk-bags/search-html

(I'll have sum splanin' to do if my wife asks why I did a Google search for, "Breast Milk Bags"!)

I already had to 'splain that one. I'm very thankful it wasn't the traditional PSK water container that I had to 'splain!

How small are they when folded up?

depends on how you fold them...however, I've enclosed a photo with rulers for size...