- I generally travel on my own, so I give a rough itinerary to my wife with check-in times noted on there. If I miss a check-in time by more than 8 hours, then she knows to worry and give the authorities a heads up (although it's never happened). If you cannot get a call to go through, you can try a text message, which apparently works on a different band and thus could go through when a call will not.
- Cash. ATM cards don't always work. Banks sometimes put holds on them if you haven't notified them of your travel plans and you use the card in multiple cities/states over a short period of time. I stopped to get gas this morning and the card readers on the gas pumps were out. The ones inside worked, but if those were down as well, I'd of used the emergency cash I keep on hand. Cash is king, as the saying goes.
3 days isn't very long...stats say you'll be fine and have a great trip, but it's best to prepare for unforeseen situations. Hope all goes well for you!