What inexpensive food gives energy and brain power?

I have an office job that is very fast paced. I find that the food I'm eating, which is usually fast food, gives me a severe downer right after lunch. I can't afford to be lethargic at work at any time.

What inexpensive foods give energy and brain power? Thanks.

Believe it or not....peanut butter! Slap some on an english muffin and the protein from the pb, and the carbs from the em, should get you through the rest of the day! ; )

Fish!

Just eat a protein bar at work then eat a big meal when you get home. Or fruits and veggies with a fat free dipping sauce. That is if its that fast paced you don't have time to go out and get a good lunch or nuke one in the microwave.

bananas