Commodities futures are just like gold based money. The gold itself wasn't traded, it sat locked in a vault somewhere. People traded receipts for the gold. I.e. that's what banknotes literally used to be.

Eh, while there is quite a lot of speculation-only trading, unless you're dealing with cash-settled futures, if you forget to close out your position you'll be expected to, say, deliver or take delivery on 5000 bushels of corn.

Commodities futures are heavily used to arrange actual exchange of goods and aren't abstractions but real contracts.

That is true right up until the day the contract comes due. Then you need to pick up your oil, pork, OJ, etc. at the time and place specified in the contract. If you holds the contract at that point in time, you are responsible for picking it up at the place in space.