Best advice I have for wreck excavation: (and yes you loot a TON of lockpicks and zipties doing this which is awesome)
Wreck Excavate in Kavala and save up your money until you can buy a cheap 1-story house on the shoreline near the excavation zone, one that can hold a medium sized crate. Once you buy the house after a few Offroad loads, all you need to do is fill your boat (NOT THE TINY MOTOR BOAT!) up and drive back and forth to your house storage. I think it's safer because your stuff is safely locked in your house and you wont lose your inventory if it was in a vehicle and it de-spawns or someone steals it. When I used to do this a lot, I would honestly dump the oil while sitting passenger in the boat because I don't think it's worth the weight : price ratio, but others think it's worth holding to sell, so I'll let you decide. I don't think its worth it and recommend you focus jewelry only and just dump everything else. This is more valid when you're using the Offroad and don't yet own the house. Once you have the house you can hold on to whatever you want until there's no room and then do large coke/oil/jewelry runs.
NOTE: Be careful when you dump objects while in the boat because the suitcase can become stacked and your boat wont move. I always put the boat in a very slow -1 km/h reverse before i start dumping things so you don't encounter that problem.
So yeah that about sums it up. My two cents, I prefer not to spend my time running to multiple vendors, I focus on selling my loot at the jewelry store only...so I dump anything not jewelry or coke... but if you're up for it by all means load all the different inventories into your truck and drive around to all the vendors; jeweler, oil/commodity trader, and drug dealer. I save my coke over a long period of time and then sell it when I have a sizable load to the drug dealer there in kavala.
All that said, jewelry speed runs are where it's at IMO.