Hollow Spy Coins
Bruce Schneier's blog links to a few sources for hollow spy coins, one being BoingBoing's Bazaar — where a nickel that can hold a microSD card costs $27. Another is Slashdot's sister company ThinkGeek, where you can get hollow quarters and half-dollars in the low 20s. As if corporate and government security geeks didn't have enough to worry about.
I was a amateur magician when I was ten or twelve, and I'll be 58 next month. You could get those coins at any magic shop way back then, or through the mail from catalogs; I owned a couple of them. Also, any machinist can and could make them easily.
Free Martian Whores!
Since these are machined out of gen-u-ine legal tender, the charge you would be worried about is defacement of currency, rather than counterfeiting.
That said, I've never heard of anybody going after currency defacement operations(even the overt ones. Those "souveneir penny" machines that crush a graphic associated with whatever attraction the machine is located in have been around for decades, and the Secret Service has shown no signs of caring) unless they involve wholesale export of coins for their melt value(I think there was some issue involving the old pure copper pennies during one of the spikes in copper prices fairly recently).
If you somehow got caught, and your hollow nickel contained a microSD card with a copy of secret_leaked_CIA_documents_that_the_illuminati_don't_want_you_to_have.doc, they'd probably throw a defacement of currency charge at you, just for completeness' sake; but, while almost definitely illegal, they aren't exactly a huge legal risk.
Probably because you are not a beard wearing Mediteranian. Random searches and such, you know.
And a nice place place would be in your laptop itself. For small things, just put them in the battery department. And for very topsecret things, open the laptop and tape it to the motherboard. Unless they realy are looking for it AND have somebody know how the xray should look like, it will look like a motherboard with some chips on it.
Don't fight for your country, if your country does not fight for you.