First of all limit your damages. Be neat and organized. If boxes are getting stepped on or run over by uboats no one is going to buy them.
Get credits from manufacturers or suppliers when ever possible. Sell item at discounts when possible. Some manufacturers offer boxes and or parts to fix items. I've never thrown out a bicycle. I order parts and repair it and sell it at a discount, but never below cost unless necessary.
Rotate perishables regularly.
Invest in repackaging equipment, such as boxes, and shrink wrapping.
Limit your damages and you can save a lot of potential shrink.