How can I enjoy a good pay month when the next one might be lean?

A $2,400 payment landed on Tuesday and I immediately opened the booking page for a $140 weekend away. Then I remembered last month's $1,450 and closed it.

I work changing hours, and those figures are what I had available after deductions. My basic monthly costs run to about $1,360. I have $800 put aside for lean months, separate from this week's payment. No hours have been confirmed for next month yet.

My sister says I'm acting as though every good month belongs to a future bad one. She has a point: I turn down plans, make it through another month, and never seem to reach the moment when I'm allowed to relax. But a strong month doesn't tell me what the next payment will be.

I don't want a budget that treats $2,400 as normal. I also don't want one where any pleasure is evidence that I'm being careless. Would you set a modest amount aside for fun each month, let good months fund occasional plans, or wait until the lean-month pot reaches a goal? How would you choose that goal without moving it every time you get nervous?