There is plenty of work out there if you are willing to look and put in the effort. We all have to start out somewhere and selling your personal items (whether they be junk or not as you say) could bring in a little revenue through yard sales and whatnot, but it is important to further your education and up your communication skills as those are what will get you into better paying jobs in the future. As for myself while I was in high school, I didn't really need a lot of money because I had no bills or anything to pay for.

I did make a pact with my parents that they would pay me a certain amount to do extra chores at home. Maybe your family will do the same if you talk to them about it.

I also had a dishwasher job at age 16 in a restaurant that I did on weekends. Like I said before, if you are willing to put in the effort you can make money. But at your age money is less important than your education, so focus that first in my opinion. Good luck on your way to adulthood!