If you can make your lunches at home on a Sunday evening, they might cost you, say, £1.50 in ingredients. Buying lunch from a deli in London might be, say £6.50 (substitute your own numbers if I'm way out).

That's £5 per day. Say you work 220 days per year (254 working days minus annual leave and sick days), that's £1,100 per year saved in that single, simple habit.

In a decade, that's £11,000. If you've got four decades to go until retirement, that's £44,000.

Assuming you instead added that £91.67 per month saved to your investments and assuming some nominal long-term interest rates (4%) and increasing your savings with inflation (2%), that would result in £148,059.38 extra in your retirement pot by the time you retire.

Depending on your FIRE objectives, that could be 5 years earlier retirement. So, just by buying your lunch at work every day, you are committing yourself to an additional 5 years worth of drudgery.

That's how I think of those little indulgences. "If I buy this bottle of wine that I don't really need, I'm pushing my retirement back a day", "If I splurge on that nice bag, I'm pushing my retirement back a month". Weighing up expenses vs how much longer it means I'll have to work has been a big mind-set shift for me.