I use rechargeable LiIon in all my lights that will accept the higher voltage, and Eneloops in the lights that won't. I have several of each charged and ready to go (beside the ones currently in service in my lights).

Still, I keep about two dozen alkaline AA's and two dozen alkaline AAA's available as backups. Alkalines have got a fairly decent shelf life these days. Several years. A bit short of lithiums, but still not bad. And they are a whole lot cheaper than lithiums. Primary lithiums are good for things like emergency car kits.