I would have thought AP could scan items in and print out some kind of lodgement receipt even if money isn't changing hands at the time.

In the meantime is it worth you designing a 'despatch' sheet and keep a list with addressee's name or ebay id, address or post code, brief description of contents and room to place the little numbered sticker from the satchel? Stick the sticker on the sheet while the employee is processing the parcels.