A friend and instructor of mine got trapped in a Pitts S2B after an on off-field landing following engine failure (you really do NOT want the engine to fail in a Pitts). It flipped, and he was trapped. Luckily a passing motorist came to his rescue and lifted the plane enough.
Since then he always carries one of those pointy hammer escape things and, instructed by his example, I keep one in the flight suit I wear for aerobatics.
My usual ride, a 182, doesn't have this problem.