I stop by the local supermarket every Monday lunchtime during work to pick up sandwich materials and fruit to cover lunch for the rest of the week.

It works out just less than £5 a week / £1 a day, much more savvy than buying lunch every day.

It also means I can eat any evening meal leftovers over the following evenings (I used to bring leftovers in for lunch), so I save time and money in that respect as well.