Valid GC but expired passport
For those of you who are legal permanent residents in the United States, a good rule of thumb is to always have a valid passport. Remember that you are a citizen of your native country and a valid passport is evidence of that. Having a valid passport also enables to travel overseas without any hitch (assuming that you have a visa, if needed, to your destination). And while your native country may allow you to enter with just a birth certificate or some other national identification document (ID), most likely you will have difficulty getting on a plane to go there in the first place from a US airport (airline staff will insist on seeing a valid passport, and visa, if neede) and it might also be difficult for you to board a plane for the flight back to America. While the CBP agent at the airport often does not even look at your passport when you present a green card, it is required that you present both a valid passport and a green card. For other purposes in the United States if you have to prove that you are a legal resident and authorized to work, even if the requirement mentions showing a passport, typically a green card alone does the trick.