Depending on where you are, there might be an age requirement for most places that offer part-time jobs. Kids your age can always try the classics: doing chores for neighbors when they otherwise can't do it themselves, asking your parents for allowance by doing chores around the house, looking for a newspaper delivery job...

I believe there are, in some cases, summer camps that you can sign up for and lead younger children for a week or so and you also get paid. My advice is to combine all of the little tasks you can get your hands on and save up. Don't spend while you work!

One more exceptional advice I can give: If you have an organization nearby that signs you up as an air, army, or sea cadet, they have summer training camps that often require you to be away from home from 2-3 weeks. They send you off to a camp base by plane (no costs on your part), and while you have fun and learn there, they also pay you on a weekly basis. The pay is quite good. When I was an air cadet, they paid up to 100 per week.