I carried a solitaire for many years as an EDC light. Wore the finish off completely so its now bare aluminum. I finally bought an ARC AAA. An AAA light isn't too large for ECD, its longer than a coin cell light sure, but not as wide, its about the same length at the key for my truck so it lays nicely beside it in my pocket and takes up less room than a coin cell light did.
I'm powering mine with an AAA Sanyo Eneloop now as my HP calculator takes 3 AAA's so I have an extra from its pack.