Some of our favorite lunches:

Bagel crackers, sliced pears, blue cheese.

Ultimate PB + J:
Sandwiched between either pita (or other hearty bread) or graham cracker.  Mix the first three ingredients ahead of time in a waterproof container for easier lunch prep.
-cashews
-peanut butter
-jam
-craisins or dried blueberries
-sliced strawberries

Smoked salmon, cream cheese, capers on bagel crackers.

Fruit cups, like applesauce are easy to have on hand as well.