Dried or dense meats: jerky (Beef is most common, but also available are turkey, chicken, and ham), pepperoni sticks, hard salami, other similar meat sticks will work as well.
Spreads: peanut butter, honey, Nutella (a wonderful blend of hazelnuts and chocolate), jelly or jam, margarine, or cheese. Most of these except the Nutella come in individual or smaller serving packets.
Grains: crackers , pound cake, flat breads (pita, Flat Out), melba toast, rye crisp, bagels, tortillas, or pilot biscuits. Protect harder or soft breads in hard sided container to prevent breakage.
Fresh cheeses: dry cheddar cheese or single packaged "string cheese" (comes in different varieties) or individual serving waxed cheeses.
Dried fruit: apples, mangoes, bananas, cherries, apricots, peaches, raisins, berries, pineapple, papaya, and others
Nuts: almonds, pine nuts, peanuts, sunflower seeds, pepitas, cashews, walnuts, hazelnuts, and Brazil nuts
Candy: chocolate (M&Ms are good), chocolate chips, licorice, jelly beans, or gummy bears (used in moderation)
Nutrition bars: Clif Bars, Power Bars, Luna Bars, Pemmican Bars, and many others
Snack bars: Little Debbie (nutter butters), prepackaged granola bars, cereal bars, and others