I use the built in eBay applet that lets me create shipping labels for sold items with the USPS postage printed on the label.
When I drag my 10 preposted boxes to the local USPS offices, the small offices will let me drop the boxes and dash, the main office insists on checking them all in and giving me a receipt. The main office claims there is some magic step/procedure in creating the labels that allows me to create and print a bar coded list of the shipped items I can simply hand them and they can scan in one pass.
I have no clue where this function under the eBay applet resides. Searching eBay has not yielded results.