You start with 1,000 Scrap. Compactors make more: switch each one on, then walk to it to collect, as each holds at most 1,000. Switch on every compactor at the start of each round. Every purchase raises that item's next price, so put the first Scrap into weapon damage and compactor upgrades rather than a stack of ammo. Corrosive (1,500 Scrap for the first one) opens locked rooms with extra compactors and traps; buy it early. Bonus Scrap also arrives at the end of each round. Keep moving in loops through the bigger rooms, so the Molded can't pin you in a corner.