The CC is a good value but a long way from the smallest possible radio. I haven't seen that card thing but it looks cute. I'd personally just go for "cheap". Walgreens has a number of junky fm-only pushbutton radios and the guts are on a small circuit board. I got a pair of them (2 for $5.00) that run on two AAA cells. Each is around 2x the size of the 2AAA battery compartment. You could probably hack off the battery compartment or even pry out the circuit board, and run it on a CR2032 coin cell. They have another one that looks like a carabiner and that runs on two button cells. Again, you could hack away the useless parts of that radio and what's left over would be pretty small. These are all earbud radios with stereo earbuds. You can separate the two wires, so two people can listen at the same time; or you can throw away one half to make the earphone stow smaller. Whatever you do will probably be overlarge for an Altoids kit, but pretty small in a bigger kit.

There was also a CPF thread a while back about micro radios, though most of the ones mentioned weren't this small.

Checking ebay, I see there are some other small earphone radios (coin cell), try searching on "tiny tunes" or "tiny toonz".