You need a budget - kind of unMustachian in a way. Having a budget of say $200/mo for dining out - just gives you license to spend $200 a month on dining! Having a budget of $500/mo for your car - just gives you license to have a shiny new car!
Until you reach financial independence, a true Mustachian would be more apt to track every dollar spent, and think of ways and alternatives to lower or eliminate each and every expense. For example, we have cut our dining out way back. We do celebrate modestly dining out for birthdays, anniversaries etc. We've cut out cable TV, Netflix and Hulu Plus. We now strictly watch over the air, or regular free Hulu for shows we missed. And we watch less TV as a result, which is fine by me.
Each and every one of us, even working towards FI, will have some non negotiable items. For us, golf is non-negotiable, although we try to make it low cost (play executive 9s, have a season pass good at 3 such courses, etc.)