Portal of Fortune: The Multiverse Merchant / Aisle of Apocalypse: Checkout at the End of the World

Colin Lockwood inherits a failing grocery store and discovers a back door that leads to other realms. He begins trading food in the apocalyptic world for gold, then strikes a deal with the cultivation realm, exchanging meals for elixirs to address supply shortages in the apocalypse. With lives tied to his trade, he shuttles between worlds to save a survivor base and build a multiverse trading empire.