Reddit reviews 4in. X 6in. Flat Cellophane Bags with Adhesive Closure - Pack of 100

First, if you haven't done it already, I would suggest getting some cellophane bags to put the cookies in. Helps keep them fresh. :) You can use ziplock bags, too, if you want.

I've shipped cookies several times without any breakage. I use these boxes, they're very sturdy and good quality.

Also, a lot of bubble wrap. Two layers of bubble wrap on the bottom of the box, a layer of cookies, another layer of bubble wrap, another layer of cookies. Usually I can fit three layers and then a final layer of 2-3 sheets of bubble wrap on top. Then I tape the box with packing tape and write the address directly on the box.

The cookies shouldn't move or slide around when you shake the box. If they do, you need to add more bubble wrap. :)

It usually costs about $16 to ship them USPS Priority 2 Day. I hope that helps.