A few days ago, I was filling a few small zip lock type bags. I was thinking there must be an easy way to fill them without getting them so full that they are hard to close and also a way to keep the zipper part clean so that liquids do not get in them.
Then the thought came to me, why not just fold the opening down one turn. Not only did it solve the problem with the zipper getting dirty and not overfilling, it also helped to keep them open, making them easier to fill.
So, the next time you use a zipper-type plastic bag, try folding the collar of the bag down one time (like you would a shirt sleeve or collar)!