Teams cannot check in to the pit stop without all of their travel documents. If they arrive at the pit stop without them, they must go back and retrieve them before they can be officially checked in. In Season 15, Zev and Justin were eliminated because they arrived at the pit stop without a passport and were unable to find it in time.
However if a team loses their passport during a non elimination round, but the following leg does not require them to use their passport to leave the country, they may proceed but must locate and produce their passport on the next leg as seen in Season 21, episode 8.