Murph's comment on the last reminded me of the way I devised to justify any extra expenditure I might ever make. A couple of years ago, I spent a day shopping for clothes and stuff. I don't do this very often, but I found myself in the mood and in the happy circumstance that everything I liked fitted and everything that fitted I liked. So I bought them.
Now, my husband has never been one of those chaps who complains when bills come in. In fact, he's very pleased when I spend money - he doesn't think I spend enough on the whole. So when I came home and said I'd been shopping for clothes, he said "Good for you." "I've spent quite a bit. A teapot's worth, in fact." "What," he said airily, "about £900?" "Oh, crumbs, no. More like £600*." "A cracked teapot then."
Since then, every time I've spent money on more than necessities, I've thought of it in terms of Lo'st'ft china. A teabowl and saucer. A coffee cup. A nice little cat - maybe not, I could get a car for that. But a badly damaged piece could start at £20 or £30, so there's something to fit all eventualities.
*This is a lot for me to spend in a day, but it may be small beer to you, of course. Or a small fortune, on the other hand.