paper route, shop assistant, sport coach or umpire, cleaner.
it doesnt really matter what you do just as long as it doesnt impede you studies. maybe try and figure out what you want to do as a career or one of your interests and talk to the owner of a company im sure they will have some after school jobs.
If you mean a good job to have during high school then I would say a job that you can show up for, make money, but get to leave the working worries there. Examples would be Jamba Juice, Starbucks, restaurants, Target, etc.
If you mean a good job to have in education, specifically high school then I would say a math teacher, some other kind of teacher, or an administration job. Math teachers are in the most demand because math is a very important core subject and every student has to do 4 and often times more than 4 math classes.