Numbness, stiffness, and pain in my tailbone that started 3 days ago. What do I do? I am in middle of long trip by charter

Get it seen by a doc. It may be due to prolonged sitting. You might try sitting on a doughnut shaped cushion to take the pressure off the tail bone. But if you truly are numb, then it could be something more serious and you should be seen for imaging studies.
Get it seen by a doc. While it is highly unlikely, there are a few conditions affecting the region of the tail bone that are serious. You mention numbness and stiffness, which are more concerning than simple soreness that is due to the pressure of sitting, and worse if you move your tail bone (coccyx) with your finger.