Great post.
I take everything inside to the main post office. Most of the time I wait in line & have them hand stamp the envelope so they don't go through an extra process. I think this misses the sorter that could tear them open. I guess still everything is supposed to go through a scanner.
I use thick cardboard & sandwich the chip inbetween. Its thick enough that on an ounce or less I have to pay the extra 12 cents for thickness. I use a regular Manila envelope usually & tape the ends. My protection is the cardboard but better chips usually get a bubble mailer too.