You can always do a patty without the bun.

Other ideas to cook ahead and take with you
Quiche: make 1 up cut into single portions then freeze, or use muffin tins

Hard boiled egg

Scallops wrapped in bacon

A sugar free beef jerky that you really have to chew.

Also make sure you have a large bottle of ice cold water with you. Sipping consistantly on that will help to wake you up and keep you hydrated. Make the car a little chilly, and listen to some music that is far from soothing.