OK. A small packet of peanuts; around 28gr or a similar sized pack of sunflower/pumpkin seeds, is my go-to emergency snack on the go. I have little bags in most of my handbags and rucksack. They don't go off or spoil, and I know I have them.
I only very rarely have a snack; I never have been a snacker, so I've tried to keep it as simple, and long lasting as possible.