Apples. Definitely apples. They're easy and grow anywhere - or, at least we can say that the exists a varietal that grows where you live. Completely hands-off to grow, they grow and fruit relatively quickly, high yield, energy dense fruit that's simple to eat, lots of sugars. Most importantly, the fruit keeps really well, for fruit. If you can keep it even halfway cool, it'll last months. The skin is edible; heck the whole fruit is edible, although most people don't usually eat the core. It's the perfect fruit. It's not necessarily my favorite fruit, but if you're taking a staple food fruit, for survival, give me apple seeds, no question.
Blackberries come in second for sheer volume and rapid growth, but they don't survive harsh winters very well, so without knowing the conditions or in uncertain environments, I'd rather have apple seeds in my pocket.