A long whistle blast sounds like a hawk from a distance, but 3 timed short blasts sound like a signal for help. Gunshots and car horns also should be timed in groups of three. Yelling is the poorest alternative. If the noise is caused by searchers, a whistle will bring them closer. If caused by animals, real or imagined, a whistle will scare them away.
Most people think of survival in terms of lack of food.
In hot climates, however, food is not as important as other factors. If water is in short supply it is important not to eat anything because it increases your water needs to digest the food. On my Australian adventure I had a 6-inch perch, a handful of wattle seeds, and 6 cattail shoots. I lost 20 pounds, but after day 3, I did not feel really hungry. Water was our biggest worry.