Gate agent may help you find an alternative, just depends on the individual and how busy they are. Always have multiple back ups before you ever get to the airport.

Don't ever check a bag!!

Alot of places won't let you through passport control until you have cleared. In the case you get through and don't clear, talk to the gate agent, there HAS to be a way for them to get you back through customs.

They shouldn't be taking a coupon from you until you are boarding the a/c. I had it happen to me once in EZE where LAN wanted to take my flight coupon at the tkt counter. I kindly asked the agent if I could hold onto it and exchange it for my boarding pass if/when I cleared and she asked her manager and he gave it back to me. Good thing too, as I cleared for an earlier flight.