Compass and topo map, also an altimeter. Lots of the country here is up and down, or nearly so. GPS is too complicated, besides that weeny little display will never equal a 7 1/2 minute topo - not to mention the battery issue. Bring spares, you say? I like basic technology that works, ALL the time.
Why not? I use film, fountain pens, occasionally a slide rule, and my typewriter is an Olympia portable that works without electricity.