I ALWAYS open the cap for the attendant kindly explaining that the cap
is cranky, the ignition key stays with the cap which stays with me
to wit I can't drive off without the cap because I have to take the
key out of the cap and I do that when I put the cap back on.

There is a short term substitute called a Plastikey that is cut by a
machine specifically designed to cut plastikeys.  AAA usually has the
machine but they may not have the proper cutting tool or the blank.

The company is/was known as Axxesss.  The "cassette" is the "A"
cassette (part of the cutting tool) and the blank is #43.

When you find the right blank at your FLAAA, get several made.  Theyre
not for permanent use but will get you on your way while you rescue
the REAL key from it's hidey spot.  It will open the syncro gas lock,
the door and start the car.

Hide your recently purchased and tested spare key somewhere on the van
that will not require tools to access.  Steve Sandlin can supply your
recently purchased key cut from a factory specification not from your
20+ old worn key.  Or if you like you can hide the worn key.

Article here: http://www.bizjournals.com/phoenix/stories/1996/10/07/smallb1.html

Pensioner.