Reddit mentions of Cheap Cheap Moving Boxes Packing Paper, Large Bundle, 24 x 36 Inches (20#)

I haven't shipped any out, but when I moved I taped the bigger ones between two pieces of really thick/rigid board (greyboard, actually, leftover from bookbinding projects). I used a bit of double-sided tape to secure it to the center of the "sandwich", and some normal tape around the edges to tension it shut. I can't remember if I used bubble wrap, but they probably ended up in boxes with other craft stuff, separated by wads of crumpled paper (this kind).

I've done some experimenting, trying things out for my etsy store more than Poshmark, and although I've happily settled on clear bag closed with a thank-you sticker for Poshmark/eBay clothes, I did like the look of using brown craft paper tied with rough twine (a roll of the paper and the twine can both be found at the dollar store). The paper made such nice creases! Tissue paper foils my best efforts and winds up looking like I am using my trash for wrapping paper.

During my last move, I had those big paper sheets for wrapping glasses, fragiles, etc. Like these: https://www.amazon.com/Packing-Paper-Large-Bundle-White/dp/B00MR7VY2W

I know I didn't pay more than $10 at Walmart, and while I was packing whenever I sold something I was just grabbing those to wrap around the item and it was GREAT. So much more substantial than tissue paper or even nice gift wrap.

I feel the lure of those adorable polymailers but until/unless this sales drought ends, I'm not ordering them. I do use white polymailers now and always scrawl a message on the outside using silver sharpie (or whatever color sharpie I come across when all the silver ones have vanished). I am exactly the kind of person who would sit around and doodle drawings all over polymailers to keep my hands busy while watching a movie or something, and if I ever get to a place in my life again where I don't have a stack of things that need my hands at all times, I will probably DIY a bunch of them one night :)