Depends on the cargo. Some gets desposed of, some is auctioned to special markets where salvagers will bid on the load and sort through it for anything still good which is then sold at resale markets or secondary markets. Some goes on sites like ebay. Some is donated to charity as a tax write off and so on.
There is no one size fits all answer to this one as it depends on product, type of wreck, outside conditions (electronics dumped into rain likely wont be good) how badly damaged everything is and who owns it. Some cargos the shipper wants destroyed regardless of how little damage for safety, reputation or liability reasons. Some would be illegal to resell. And some just wouldnt be worth the trouble.
