Brown bagging --yes! We have a decent cafeteria at work, but for the price of one or two lunches there I can make my own for the week. I have a file drawer stocked with canned soups and beans, sardines and tuna, rice noodles, oatmeal, dried fruit; another drawer with spices, dried onion, bowls and utensils, and numerous condiments in the fridge. Bring in some fresh veggies to be nuked in some soup or made into a salad, and I'm good to go.
My frugal feeding habits also include keeping an eye out for potential leftovers from catered lunches at work. Management-types gathered in conference rooms all morning often means lunch leftovers in the commons area around 1:30. If I can get there before the feeding frenzy hits, I can usually bag a complete meal for the next day.
Something that always baffles me at work is the nearly constant stream of folks buying snacks from the vending machine. $1.50 for a tiny bag of Doritos...really?! Why not get a giant bag at Costco and bring in a handful each day? Maybe it's self-imposed rationing on the junk food?