charges for shipping [something] and for wrapping and handling the item. The cost of the book was quite reasonable, but the postage and handling was outrageous.They did not charge postage and handling because I prepaid the order.
fit/write something on the back of a postage stamp
if you say you could write what you know about a subject on the back of a postage stamp, you mean you know very little about that subject What I know about car maintenance could be written on the back of a postage stamp.