Munching a lunch you brought from home is one of the best ways to keep food costs down. Packing a variety of lunch foods will keep you from abandoning your brown-bag system because of boredom, and if this is already getting old, give yourself a break and designate one day a week for buying lunch.
You should only consider adopting this system if you can afford to buy one lunch each week. If so, make it a day like Wednesday when work seems to pass like molasses. My trick? I keep soup in my drawer so that I have an option if I'm not in the mood to splurge on my assigned day. That way, my lunch-out day isn't wasted.
Setting up one day for buying lunch can motivate you to bring lunch every other day, and gives you something to look forward to — a small price to pay for a little boost in your work week.