USPS logo on packaging display, APC in background
The Post Office has also been selling their own supplies under the ReadyPost brand, which are available only while the Post Office retail windows are open. This product line, which is surprisingly reasonably priced when compared to local stores, is likely a response to the consumers that come to the Post Office without packaging and want to mail something at First-Class rates.
The line of ReadyPost products sold at the Post Office has also widened to include not only boxes but bubble mailers, bubble wrap, cushioned mailers, tubes and plain envelopes of all sizes and shapes. While I imagine the sale of ReadyPost is not as profitable as giving away "Priority Mail"-only packaging, it fills the need of specific customers and provides them a convenient and affordable mailing experience.