"John Harper"

Lighter than a hammer and a lot more effective, for glass anyway (never
tried it with Plexiglas)... an automatic centre punch (one of those things
that you push until it goes "thunk" and makes a dimple in the metal).
Press it up against the corner of a window and bingo. (I have a good
reason for knowing, honest, I locked myself out of a rental car once
and this was how they got back in).

Somebody joked about putting a Ka-Bar combat knife behind seats in airplanes
here this week, but it's a good point. I always carry mine, even in my jeep
or van. The blade of a Ka-Bar is sharp enough to cut fabric and the back of
it is a metal pommel that is flat for pounding tent stakes, and it could
easily be used to break a window.

And unlike a hammer or a centerpunch, it's great for slicing summer sausage
and cheese. :

A Leatherman would probably do too. I carry a small flashlight, some
aspirin, a yak-sack that I liberated from a United Airlines seatback, a
knife and glasses.

Personally I'm pretyt impaired without glasses - I can fly just fine but
I can't read anything. I keep a spare pair of (cheap) glasses
in the plane and another in my flight bag.

I usually wear contacts. At my first BFR, the CFI told me he'd sign me off
if I promised to carry glasses with me "in case." (pun) Made sense, so now
I almost always do.

-c