Yes, we brown bag a majority of meals. Variety is key. Find foods you like and them change them up enough to keep things interesting. Besides the cost savings, you also have the opportunity to eat healthier thay you might otherwise. For instance, breakfast might be a banana or apple and a granola bar.
If you have a garden, grow things like lettuce (rocket is good), chives, spinach, Welsh onion and tomatoes. During the summer you can pick enough to make a salad for your lunch box every day or nearly every day. Add interest with things like cooked pasta or rice, tuna/mayonnaise, olives, ham, left-over cold roast chicken, grated Parmesan, cheddar cheese (though not all at once perhaps...).