You both have good points.  Your wife is right that eating out is a much more expensive way to (merely) eat lunch than to bring a bagged lunch from home.  But you are right in pointing out that you view eating lunch out as more than a way to “eat.” You use it as a form of social networking with your colleagues, and I suspect the quality of that interaction is at least slightly different from the kind you have over official meetings at the office.

So, I would suggest a compromise. Consider the extra cost of eating out over bringing your lunch as part of your “extracurricular” expenses and reduce the rest of your “fun” budget accordingly.  For example, if you’re spending $7 extra a day on lunch out, you should probably not do happy hour every day with your colleagues (or at least do one fewer drink than otherwise!). Or, you should take the $35 extra per work week and take it out of your (personal) recreational expenses for the weekend.  But don’t take it out on your wife by effectively taking it out of your shared “fun” money.