Let's say that civilization ends due to non-globally destructive means. For instance, a rising tide that destroys ports and trade wouldn't scar the landscape of Denver the way nuclear war would. Economic collapse or riots wouldn't change the climate. Please, nobody mention zombies. The result is people living essentially in anarchy until a new power can come maintain order.
Centuries later, a new civilization begins to rise, but they haven't yet built an industrial base or trade network. Working factories are minimal and there are few comparable civilizations with which a trading relationship could be established. What specific obstacles or resource deficiencies would they most likely face in the first decades of trying to rebuild?
For instance, there would likely be plenty of aluminum from recycling to eliminate the need for mining more in the short-term, but the civilization would not likely have access to citrus unless it was within a citrus growing region. The civilization would not be able to build new skyscrapers, but it would be able to make passable replacement glass for windows at high cost.