LED beanie hats. One with surprisingly good circuitry.
LED beanies are apparently a thing. So I bought a couple from China via eBay to try out. One is really bad and one is surprisingly good.
Here's a generic eBay search for the good type.
http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&LH_BIN=1&_nkw=rechargeable+LED+beanie&_sop=15
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