I'm pretty strict about my finances, and my friends and coworkers refer to me as stingy because I'm always calculating costs and rarely impulse buy. But every week or so, if I don't use all my "spending cash", I'll take some of what's left over and put it in a lockbox, to use on a 'rainy day'. There's roughly $1000 in there currently, so I'll take a chunk out of it to buy an Apple Watch, if I decide to get one (still unsure!)
I wouldn't put it on my credit card, not because I think it's a sin to charge stuff but just because I HATE having one extra bill to pay at the end of the month.