It's called trail mix for a reason. Make your own at home using whole grains like granola, nuts and dried fruit. If you have a sweet tooth, some chocolate chips will add simple carbohydrates and give you a bolt of energy.
A combination of tuna and crackers is a protein and carbohydrate powerhouse. Plus, it's really simple to bring along. Take along tuna with a pull open top or in a tear-open pouch, and you're good to go.
Peanut butter is one of the most versatile foods on the planet. You can smear it on crackers, or you can eat it straight out of the jar. It pairs well with your trail mix, and if you're adventurous, it may pair well with some of your other snacks. Either way, it has a lot of protein and good fats. The nutritional value is even better when paired with a carbohydrate.
This may seem like a counterproductive snack, but the high calorie content of candy will give you a quick energy boost. Candy containing nuts are ideal, such as Peanut M&M's, Snickers and Pay Day.
Those looking for an alternative to candy bars should pack a few LUNA or Cliff bars. These are slightly more expensive than candy bars, but are much more filling and have a high calorie content for those exerting a lot of energy on their hike.
Jerky and dried salami are good choices to increase your protein intake. Dried meat will also keep and fare well in any extreme weather.
Cheese has all the nutrients you need on the trail, including fats, carbohydrates and proteins. Hard cheeses like aged gouda or aged and sharp cheddars will travel well unrefrigerated.
You'll want to pour a little olive oil on many of your snacks to add more fat to your diet. Olive oil will also help any intestinal issues or constipation you may experience during your trip.