As a shipper I used to try to make packages as small as possible but they bill you by volumteric weight so if you are shipping heavy stuff, the size doesnt make a big difference if at all. And there is a floor price as well for smal items. Now I put them in boxes at least large enough for the lablel that CanadaPost puts on there. I also add a hand written address on the side of the box in large font to help the mailman see it better. Less chance of a mistake this way because the font on the printed label is tiny.