It is possible, but not easy, to eat healthy at fast food places. Order a hamburger PLAIN. You’ll get lean beef and a bun–necessary protein and carbs. Skip the mayo-laced sauce, gloppy cheese, fries, soft drink, etc. Bring your own apple or orange for your “drink”, or get a free water, maybe your own peanuts, and voila, a complete meal for under $2.
The downside is the dirty looks from the order-taker.