Cataclysmic Apocalypse: Starting by Saving the Older Sister Next Door

(Multiple female leads, multiple female leads, multiple female leads. Important things must be said three times!) Xiao Feng drowned while trying to save a boy who had fallen into the water. When he opened his eyes again, he discovered that he had transmigrated to a water-covered planet extremely similar to Earth and awakened the Doomsday Shop System. He learned that the apocalypse was coming and temperatures would plummet, so he used the supplies in his starter pack to build a warm shelter, stockpile supplies, and take his neighbor, an older sister figure, to safety. A beautiful young wife asks me for food. Sure, but what will you trade for it?