Answer:
My second is performed by my first, and it is thought a thief by the marks of my whole might be caught.
Used left or right, I get to travel over cobblestone or gravel. Used up, I vie for sweet success, used down, I cause men great duress.
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.
I can sizzle like bacon, I am made with an egg. I have plenty of backbone, but lack a good leg. I peel layers like onions, but still remain whole. I can be long, like a flagpole, yet fit in a hole.
When I'm born I fly. When I'm alive I lay. When I'm dead I run.
This food is a tortilla filled with cheese and sometimes chicken before being heated or cooked.