Stay on track with a topographical map and compass. A GPS is a great additional tool, but always pack extra batteries, and carry the map and compass as backup.
Stash a few spare trail bars or other shelf-stable snacks in your pack in case you’re stuck out longer than you planned.
Get shades with UVA/UVB protection, a hat, and broad-spectrum sunscreen of at least SPF 30.
Carry waterproof matches and/or an extra lighter, plus emergency tinder (dryer lint or petroleum jelly-dipped cotton balls work well).