Pilot.
Oh wait, not that kind of a tool.
If 12V plane, bring a lithium jumpstarter pack, especially on longer trips to remote airports. Doubles as a phone charging pack. If 24V, do some research and see if you can find one.
Small handheld radio, with a cable that allows it to operate/charge from the jumpstarter.
If operating in a remote area, bring clothing/24h survival gear appropriate for the conditions.
On the topic of survival, and foods to bring, here's some useful info: metabolism produces about 110 grams of water per 100 grams of fat, 42 grams of water per 100 g of protein, and 60 grams of water per 100 g of carbohydrate. Protein metabolism also generates a lot of urea, requiring even more water to flush it out.
In plain words, don't rely on high protein foods for survival purposes, they'll dehydrate you very quickly if water is scarce. Fat is the best, but most fats don't store well for long duration. Sugar is a great survival food with a very long shelf life, so if you're going to rely on one survival item, bring half a pound or more of cubed sugar with you.
Slightly less on the longevity scale, but probably the best survival food overall when water is an issue, is chocolate. A good mix of fats and sugar with minimal protein content, it will produce about 50-60% of its weight in metabolic water. Best form of survival chocolate? M&Ms, or similar sugar-coated pieces. The sugar coating keeps the pieces intact regardless of how hot it is outside.