A small AA-battery light is fine. Its most important use is for reading a map, and perhaps for signaling. You will probably find that if it is absolutely necessary to walk after dark, starlight alone provides enough light once your night vision adjusts and you are sure of your footing. Sunglasses and sunscreen. These might not be critical for wandering through the Eastern woods, but they are absolutely essential for survival in deserts, on snow, or in high mountains above timberline where the atmosphere is thin.
Sunburn can lead to severe dehydration.
The same conditions can cause snow blindness, a particularly painful, though usually temporary, condition that can occur within less than an hour's exposure, though the symptoms may not show up until eight hours later. Matches in a waterproof container. The wooden strike-anywhere variety is best. Just be sure to store them in such a way that they cannot rub against one another and light themselves. An airtight pill bottle or film canister will keep both oxygen and water out.