I make two meals per person each night Sunday to Thursday. We then have the leftovers for lunch at work the next day.
Given that I need to prepare and cook food for dinner anyway, doubling the veg prep and cooking quantities doesn’t require much more effort.
I’ve implemented this trick at home and we’re saving anywhere between $70 and $170 a fortnight on work lunches as a result. This adds up to between $1680 and $4080 a year!