Hello! Can I travel within the USA if I have an overstayed visa ?

When you overstay your visa you are not safe. People who are out of status do use planes. I don't know what proportion of them attract the attention of the authorities and end up in removal proceedings. Since I don't often visit people in detention, I only get to see those who have taken the risk and survived it. Wherever and however you get married, congratulations.

Get married in your current city and state, file the paperwork to update your status and then go to Vegas.

Don't worry. No TSA employee at the airport security check lines even knows what an I-94 is (or cares..) just travel on your still valid national passport and you won't have any problems. Unless you are currently traveling to and from a Texas border town airport there are no immigration checks at US airports. I promise you. To test the system (and be able to better answer your questions here) I recently took the flight from Los Angeles to Boston's Logan airport and back on my valid Italian passport issued by a US consulate in the US. with of course, no US visa entry stamp on it. All the TSA agents simply gave it a cursory look at the picture, at me than at the picture again and whisked me thorough the security line in no time.. Las Vegas is a great place to get married!

In my opinion it is not safe to do that.