I have one public schooler (14), and two hsers.
I have paid $100 for my schooler to play in the music program for the year. (Thankfully we do like & respect the amazing program). He's using the same LL Bean pack I bought him 5 years ago when he was hs'd. (All my kids have the same large pack).
I bought a music photo of his program, with one of him alone playing one of his intrsutments. I thought I wasn't going to, but dang, he looked cute (Grrrrr). That was $25.
Supplies-
Paper, pens & pencils. 4 3 ring binders. Around $25? He uses a calculator. but our family already had several different calculators, & I am not sure which one he uses for school currently.
He brings his lunch from home.
Plus, I've donated $100 to the music program. Sometimes in the form of outright checks because I think they are so amazing, and sometimes cash for some fund-raising baked goods at events and town GC booklets (for various discounts at local book stores, shoe stores, restaurants etc).
Let me know if there is a hsing thread asking this question. Or maybe not.

I probably don't want to add that up.

ETA: You wanted extra curricluar, which I didn't realize at first.
Year 'round: $100/mos music lessons, sometimes more, if he is wanting that. Sometimes less , depending on need. We do private lessons. (He is a musician; it's his passion & he plays a few different instruments. We think what we pay privately is bargain, and he does get daily music lessons at his public high school, which is his second main reason for attending).
$100 for town baseball (Summer)
$100 for town tennis (Summer)