As there are no EU rules on travelling without a valid travel document, conditions and procedures vary widely from country to country (and may change without notice). If you have already set off on your trip and you’re in the EU, your first port of call should be your country’s consulate or embassy.
Bear in mind that, even where some countries allow you to leave or enter their territory without a valid travel document, you may still need to show one in countries you are transiting through.