Compass...neck lanyard Silva whistle compass. Simple and light, hard to find these days. Learn orienteering. If you have a map, you only need to know where mag north is.
Thermometer...which I find useful, simple zipper pull that stays on my pack.
Altimeter/barometer....I used to carry a Thommen Everest. Best mechanical hiking barometer made. Now, barometers show up everywhere. Watches, phones, walkie talkies, gps. I've got a Brunton Weather station thingy that does wind speed, temp, baro, altitude, all in one tiny package. Many watches have all that. Barometers/altimeters are useful for hiking in the mountains and finding yourself on the map if you don't have gps or visible landmarks. Predicting weather is very tricky with one, especially when moving around. Barometers usually stay home.