The large ones are the right size for $5 slot tokens. I have several hundred for my collection and have not been able to find more in the past several years.

By the way, a carton of plastic pages will fit in a Priority medium flat rate box and postage is around $12.

Also, in case you want to protect yourself from inflation, you can buy Prepaid Forever Priority Mail Medium Flat Rate™ Boxes from USPS for $12.25 each (minimum of 3). Rate is good forever, just like 1st class stamps. No guarantee the USPS will still be around to deliver them in 10 years, though .