When I save money on a necessity, I give myself a shopping credit. Then, when those fabulous shoes walk in, I buy them guilt-free.
Of course, the credit doesn't have to go toward delightful but unnecessary (and OK, probably excessive) accessories. The credit could go toward travel, alcohol or, heck, if you're really good, charity.
Taking the Tube to Heathrow instead of the Heathrow Express? There's your glass of wine at the airport. Taking the Heathrow Express instead of a cab? You're halfway to a wallet at Bally. (Taking a coach might seem a bit extreme, but you can get around for cheaper with a coachcard, so that trip to the airport could earn you anywhere from a second glass of wine to a full case.)
In order to maintain my shopping fund, I do make an effort. If my coffee, toothpaste or mascara is on sale, I buy enough to last me a year. (£35, £20 and £15 in the fund!) If a a good brand of olive oil or Dijon mustard is on sale, I'll buy three. (I won't, however, change my brand of loo roll, ketchup, or conditioner, regardless of the savings.) If I'm booking dinner out, I'll check out a deal site like Virgin (which are currently offering 20% off experiences in the city), and if there's a place I like, with dates that work, I'll happily save £50. (In the fund!) If the parking garage lets me out without paying due to some crazy glitch, that definitely goes in the fund. (£18!)
My husband doesn't buy this line of thinking at all. "So how does it work when you find a new winter coat for £300 instead of £900? Do you then give yourself a £600 shopping credit?" No, I say, that would just be silly. In that instance, I'm stoked about the deal I got and the lovely coat for which I would never have paid full price. But when dishwasher tablets, Crunchy Nut or bottles of San Pelligrino are 3-for-2, I throw a few quid in my imaginary fund.
There's one area with which no one can argue, and that's when my weekly house cleaner cancels. In that instance, I spend two hours cleaning, then march myself right down to Harvey Nicks. (Who am I kidding? I don't go to Harvey Nichols.)
I suppose the day I start actually keeping track of my shopping credit will be the day I stop having fun thinking like this. But for now, it allows me to keep it all running in a somewhat acceptable manner. And for that, my shopping credit surely deserves a small deposit.