Rechargeable lithium batteries and red mode

Do that.

The quickest improvement is switching to rechargeable lithium AA/AAAs (like Eneloop or IKEA Ladda). They hold voltage better in cold weather, don’t self-discharge as fast, and you can carry a small solar panel or power bank to recharge them on a long trip. A headlamp that takes standard batteries makes this easy.

Red mode is the other big one. Not because red LEDs are inherently more efficient (they’re not), but because