You can do a lot of things! A road trip, a day off work, treating yourself to a manicure or pedicure or new clothes, jewelry, or redecorating your bedroom.
Personally, I told myself if I didn't cut on my wrist for six months, I would get a tattoo there because I'd always wanted one. And I also said I had to work on not cutting anywhere else as well (but I said the wrist first because it's where I do it when I'm suicidal) but I would not make myself stop cold turkey for the tattoo. That way, if I cut on my thighs or something, I wouldn't feel like a total failure, and I could reward myself for alleviating one part of the problem. And I REALLY wanted a tattoo, so it worked. I went actually closer to 9 months before I did it, and now I've got a tattoo right over my scars that says "tempus aurum" (time is gold in Latin) with a semicolon under it. (Look up the semicolon project for suicide awareness; that's why I did it.) It is actually a good reminder to me, both when I want to cut there and when I'm just down. I don't know how you feel about a tattoo, but that's what helped me.
Congrats on your progress! Definitely reward yourself somehow. You deserve it.
“Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid.”