I work in a major metro downtown. Lunch out here is $10 at a cart or fast food joint and forget about sitting down to eat. That's $50 + dollars a week. But I HATE leftovers and I'm terrible at remembering to bring lunch (I can barely function in the morning to remember the bottles let alone lunch) so this one place I realized I could make a dent in my weekly expenses.
How? Well, about every other week I leave 45 mins early (planned ahead so my husband can take the kids.. yadda yadda) and go to the grocery store. I stock up on yogurt, cereal, lunch meat, bread, hummus, soups, etc. and I use those to make lunches at work. I don't have to "know" what I'm having that day as I have a mini store in my office and I still treat myself about once a week to meal at a cart or an extra snack or hot chocolate.
I'm not just saving more, I'm cutting down on take out food waste that would go to the landfill and I'm most likely eating healthier to boot. It has taken me about 6 weeks not to truly make this a habit - so I encourage you to try it for about 6 weeks and see how well you do.