A flashlight.

Whenever and wherever I travel, I keep a mini-mag light with me, along with spare batteries (and bulb in the handle, as is standard). At night, it says on the nightstand next to my eyeglasses, within reach at all times.

I don't travel much anymore, but today I think I would add (not substitute) a LED head lamp. [/quote]

Both torches should be L.E.D. The bulb on a mini-mag is only rated for a few hours and by current standards, the battery life sucks. Most pocket L.E.D. torches at the same price point have vastly superior performance.
M
Just to reiterate a point for newer members: It it advisable to ensure that they use the same batteries, and you have at least one spare set for each. No great hardship if they are both AA/AAA.