My favorite sandwich is a sandwich they don't have on the menu anymore. For 10 years, I would always have the 3-cheese Grilled Cheese Sandwich at the Toasteria Cafe' in Taipei, Taiwan. Now they changed it to the 4-cheese Grilled Cheese Sandwich, but it's taste is very different.
I would travel back to America, lay in bed at night, and dream about going back to Taiwan to eat that sandwich. Luckily, the manager at one of the newer shops was at the original location (it was once just a tiny shack with several tables and chairs), and he makes the original sandwich for me.
If I would have a last sandwich, that would be the sandwich for me. And I would enjoy every bite...