Healthy, Quick, Snack

Nuts - I like whole, unsalted almonds - I toast and season them myself
cheese sticks with some whole grain crackers
yogurt
whole grain bread with peanut butter
granola bars (there are many good ones on the market that are lower in sugar)
Apples, pears, grapes, strawberries, banana - all pack well
Hummus and pita bread - they make individual cups of hummus
whole wheat tortilla with melted cheese
Hard boiled eggs
turkey slices rolled up with cream cheese

It is important to get breaks in the day - so not sure what kind of work you do. Try to balance a complex carbohydrate with protein for "staying power"

ants on a log..celery with peanut butter ans raisins
100 calorie snack packs

Nuts are a great snack. I keep almonds and cashews on hand. Just a little handful works wonders.

Peanut butter is good as well. Put a little on whole wheat bread.

Instant oatmeal. You can have it made and eaten in 5 min. start to finish. It transports easily, and is nutritious. You can dress it up a bit with a little cinnamon, nuts, and drizzle of honey.

Apples or Pears with Peanut butter, the fruit gives you the quicker energy, the protein will last longer. Bananas are great too.
Any kind of nuts work as well for a longer boost.

Try to avoid any heavy carbohydrate like crackers or chips, the energy won't last, not to mention slightly unhealthy.