Pretty recent. Not long ago I moved from Idaho to Montana, and during the move I found a long-expired box of Cayalume sticks. I've been snapping one occasionally just to see how they've held up and the results are encouraging.

Still, a few knocks on the light sticks; as you say they're a one-use items. Next even on sale they're $.50 or so each for a single use. Lastly they're light but somewhat bulky. In a very small kit I sometimes can't fit one in unless I remove the outer wrapper which I'd rather not do.

Have you tried the mini versions? They're around 1.5" long and still pretty bright. I will often carry a vial of them to mess around with as markers.
“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman