Back in the day, I had a classmate that would steal those gaming laptops and mice from Walmart and sell them on eBay. The anti-theft tags that they put on them just slip off so he would bring a backpack and grab a few and sell them.
I made more that $1000 selling weed in high school. This wasn't something I ever did regularly, just occasionally when I had weed I didn't want. I would sometimes sell oregano to middle-schoolers and tell them the strong herbal smell was indicative of good weed. They would pay $50 for a couple grams of oregano.
I have bought slightly broken guitars for very cheap at pawn shops, repaired them and sold them. Pawn shops are willing to negotiate on busted cheap guitars because they take a lot of space. A little wood glue and sand paper and a new set of strings is all it takes to make a $50 profit.
You can buy cheap things on a bulk order site and sell them. Pocket knives you can buy for cheap and mark up quite a bit. Buy a few $5 knives on Amazon and sell them for $10 or $15. Kids your age love that shit.
It's a lot harder to make $1000 as a teenager than an adult. Good luck