I encountered this word this morning for the first time, reading The Cutting Room (Welsh, 2002, 226), where valuable books were being retained by the dealer, and not destroyed as he'd promised, he regarding them as "legitimate pochle".
An online illustrated Scots dictionary gives the meaning here. The OED is less certain, giving it as a variation on packald, which is a bundle, a package, (with the subsidiary meaning, the postal service).
Welsh, 2002. The Cutting Room. Canongate. Edinburgh.