I’ve carried an Arc AAA since the Loma Prieta quake — it’s just the right size to fit in a velcro triple fold wallet and attached to the wallet fabric with a little clip. an Energizer primary AAA lithium cell lasts many years.

There are newer and even smaller AAA lights. Someone will be by in a minute with pointers (or you’ll find the Search tool here quite responsive)

http://budgetlightforum.com/search?q_as=smallest%20AAA