For day hikes or extended backpacking trips, summer or winter, my usual trail lunch is some kind of hard sausage (hard salami, sopressata, etc.), cheese (sharp cheddar, usually), and crackers of some sort. Sometimes something green, cucumbers, celery, pickles. Come to think of it, that's often what I eat for lunch at home as well. Candy of some sort is especially good in winter when you need extra sugar energy.