Been hording machinery for salvaging & surveys, ran low on money in the core and stumbled upon a contract for machinery, and it felt really good to go sell off (at a high profit) stuff I've been hording for gameplay reasons without having to go trade for the needed good, which made me think of how other resources could have some token use so you could justify ever having on you enough of a thing to fulfill a contract that comes your way without having to buy it, and I realized there's a really simple way; supply alternatives, OR, emergency logistics!
Run out of supplies and your crew eventually dies off, repairs stop and your ships break down. If you run out and you're hauling a planet's supply of food, instead of an accident killing crew (ever) it takes your food, at an increased rate so it's not cost-effective long-term as an alternative to supplies but in an emergency is better than losing crew. If your fleet is badly damaged and you run out of supplies, metal can be used to continue to repair hulls and slow CR decay without recovering combat readiness, requiring that you have at least a single machinery as a catalyst (so if you run out from accidents eventually then all the metal in the world will do you no good), and if you're running critical, like stranded on the outter rim, you can run rare metals and machinery as a catalyst to consume food, organics and metal at the same rate as you would supplies (3x the cost-per-day, not factoring in dollar worth) to halt all fleet degradation from supply shortages at the expense of suffering accidents as if you were low on supplies, so that eventually the emergency supply-manufacture you're running onboard your fleet, which explodes periodically because it's incredibly unsafe to do in space, eventually consumes in an accident the last of your rare metals.
None of these would even come close to replacing supplies, or make an expedition fielded without supplies feasible, but would give you reason to stock up on cheap food if your supplies-fund doesn't quite get you far enough to make your expedition safely, and if you run short along the way you could take the garbage-cheap scrap metal you've been picking up along the way and if you carry some rare metals you can stretch your fleet out on the way home, and maybe find after you've gotten back that you had an in-game reason to horde these otherwise worthless (in gameplay) resources, happen upon a procurement contract and get rewarded for your cautious hording without having to go ply the stock markets to do procurements, giving combat-only or war-only or salvage-only players a chance to do procurements.