It's also very unlikely you'll need to escape a plane. This entire site is a discussion of unlikely scenarios.

The issue of being able to get to shears is solved by wearing them around your neck on the plane. I've flown with other essential survival supplies around my neck.

The thought of burning alive freaks me out enough to wear, around my neck, something that can cut a belt. A small man bag works too. My Maxpedition Remora swings around to rest comfortably on my lower chest.