Let's be clear: poly bags are simply plastic bags.The name "poly" is a descriptive term that is used widely in the packaging industry, but to the everyday person they are just plastic bags.
Just about anything you can think of can be put into a poly bag. The question to ask yourself is "Do I have sharp edges that could pierce the plastic?" If so then you need to select a gauge, or thickness, of plastic that is 75µm and above.
The bags come in 5 different thicknesses:
Just click on the link to any of those and it will take you to the individual price list for the gauge of each bag. Using a heat sealer to seal the opening ensures that your goods stay inside the plastic bags. Otherwise you can apply packaging tape if tamper-evidence is not necessary. Stapling the poly bag shut is another option, but the safety issue of fingers getting caught on the staples can be overcome by applying a strip of packaging tape.
Some companies pack their goods into the plastic bags and then heat seal them shut, however to actually despatch them to a client, they then in turn put the plastic bag into a courier bag. There are 7 sizes in the courier bag range and once these bags are sealed the only way to get them open is to cut them.
If you're after zipper bags you might see around school's have a look by clicking on that link. Or if you're after carton liners, then click on that link to have a look.