If it had to all just me on me. I get my nails and eyebrows done once a fortnight (usually), so I'd put the money away to pay for my appointments for the next few months (exactly how long for would depend on how much other things cost).
A few years ago for our second wedding anniversary my husband and I went to see a show and stayed in an amazing 5 star hotel. We loved it and said we'd go back for a significant wedding anniversary in the future. At first we said 5 years (didn't want to wait too long), which would have been this April. Obviously that wasn't possible. So we are now hoping for 10 years. So I'd put the money for that away now so we had it ready.
Finally years ago I got my hair permanently straightened and I loved it. If I could I'd get it done again. Not a Brazilian blow dry or keratin treatment (not sure if they're the same thing or different? that last 4- 6 months or so I've been told. This was permanent Japanese hair straightening that that took about 3 hours to do, it cost between £200-£300 and lasted until it grew out completely, which was a good year and a half maybe more. I hope I don't offend anyone, that's what it was called at the time and I'm not aware of any other name for it. Unfortunately I can't find anywhere that does that treatment, only the others which I'm not wanting to have. But if possible I'd have that done again. Was the best money ever spent. I loved it.