Do you loose everything in the usage area at the end of the turn?Yes
For example, if after I activate my supply track I have a wood and two gold in my usage area, can I skip the use metals step, build a camp with the wood, and save the two gold for a later turn to buy a more expensive investment?No
Or, if I have two wood in my usage area, can I spend one now to build a camp and save the other to build a camp later?
The gold is wasted.
Finally, if my usage are only contains a gold but my gold shipment track is full is that gold wasted or do I get to save it for later?