Because it's always handy to have an anti-corrosion universal lubricant around, and not only is it small enough to keep in a purse or a backpack, it's also not a pressurized aerosol. (It's more like a felt-tip pen.) This is very, very important, because aerosol products tend to go boom if they get too hot, and I frequently leave my kit in the car when I don't feel like hauling it inside a store. Also, aerosols tend to lose their fizz over time. This is a very good thing to have, with lots of uses, negligible weight, and only costs a few dollars. Weirdly, I couldn't find this at my local supermarket or discount store; I had to go a hardware store to get it, and it was lurking in the "impulse purchase" section near the register instead of with the rest of the lubricants.
2) Solar-Powered Water Bottle Cap
This is pretty much the embodiment of the Z Kit philosophy: For zero extra space and practically no weight gain, you turn a water bottle into a lantern. You gain function AND it requires no batteries. Fill it up, turn it on, and the diffraction of water scatters the light so that you have a lantern. Brilliant!
As much as I love ThinkGeek, you can buy it for $3 less from GoFASTandLIGHT.com.
Have you seen any cool new gadgets that deserve a place in my Z Kit? Let me know!