Contest: What should David take to Mars?

[davidlevine]

Over at the I'm going to mars! post, azahru points out that the ill-prepared character is often required to take command at some point, and martianmooncrab says "don't forget to take that random item that will save the mission and endear you to the Martians." threeoutside took that ball and ran with it, suggesting that it would be a cool contest. Why not?

So what (small, lightweight, inexpensive) random item should I take to Mars? threeoutside suggests a good old-fashioned church key, and beamjockey suggests an empty Burma Shave jar. What's your idea?

Winner gets a signed copy of Space Magic and an actual "Mars" rock.