I once had to tear my way out of a denim jacket that I'd managed to zip up, but had got the zip firmly stuck and unable to be brought back down. I did that by hooking it onto a small-ish closet doorknob, and managed to tear the seams (it didn't tear any of the fabric). I repaired it and reinforced all the major seams after that.
It seems to me that the ideal weapon for getting out of that thing if the buckle jammed would be a hook knife mounted to something at a convenient height. Something like
this, attached to an L-bracket and screwed to a vertical surface. You'd need to be sure it was well attached, because you'll need to put a fair amount of force on it to cut the fabric.
I'm not a fan of loose knives or scissors - when tied you don't have much control over a thing with a long exposed blade and the amount of damage that can do when (not if) you lose control of it is considerable - I know,, I have the scars. Having your blade pointed away from your body and attached so you only have to control the fabric you're trying to cut is going to be a lot safer. Not perfect (it is a Plan B), but less likely to open an artery...