You will never have more spare time then when you're on your summer break during school. College, high school or even younger you can take this time to sharpen your skills as an entrepreneur. If you have any interest in running your own business someday this is the perfect time to see if you have the talent to be successful when school is over. As a bonus if you hate school that is one of the most common traits among successful entrepreneurs. It's also true of gang bangers and fast food workers, so get as far as you can in school before you start the next billion dollar app.
There are a lot of small businesses you could start during the summer but unless you're done with school already they are going to be hard to keep going once you go back. If you want to run a small business just for the experience there are some options. You'll probably have to leave everything behind once school starts again.
The best ideas for a small business are things for your town or city that are successful elsewhere and do not exist in your city. Starbucks pivoted because the CEO went to Italy and discovered how everyone loved high end options and a casual environment they could relax in. When he went back to Seattle, Starbucks and coffee as we know it completely changed in America. Have you been on vacation or lived somewhere else and noticed an amazing local option that everyone loved but doesn't exist or is poorly done in your city?
This doesn't have to be anything new, just a spin or new angle on something that already exists. We had coffee shops before the Starbucks revolution but our best options were usually a diner or a convenience store and with either option you were going to get black coffee with creamers and sugar packets to mix yourself.
If you have been somewhere outside of your local area and noticed a small business that was doing really well and it's something you're passionate about you could have a business that grows quickly. Once your summer is over you'll probably have to stop for school but it's something you could always go back to if it's successful enough. Even if it's not successful if you plan on entrepreneurship after school this experience will be better for you than an MBA at any university.
A startup is probably going to be easier for you to start than a small business. It's something you can also keep going while you're in school. While a small business is going to need your time and presence in the local community a startup can be done from anywhere at anytime. Let's face it if you're startup is successful and you have a passion for it you will still have plenty of spare time to work on it when school starts again.
The best ideas are problems. Look for things that people or businesses need help with and is something you can monetize. Uber found that the taxi system was outdated and unpleasant for customers but was also a huge industry that wasn't going anywhere. They were founded in '09 and within 5 years were valued at $17 billion.
The ideal startup has 3 founders. The hustler, who is out promoting the company and running marketing and sales in the early stages. The extroverted people person. The second founder is the product guy. This is the person that will be focusing on the day to day operations and making sure the product is the best possible. The third founder is the tech guy, you can probably find him in some dark basement hoping to get a girlfriend before he turns 30. Anyways these 3 different types of genius will probably not be hanging out together. No matter which on of these 3 you are you're going to have to be creative and step outside of your normal circles to find the other two ideal founders.
Now that you have your founding team you're ready to go full throttle. Disagree about something, everything? You have three founders for a reason. 2 out of 3 votes wins. You can quickly move on to the next problem.
This is just the tip of the iceberg for the type of businesses you can create during your summer break. Going to work for someone else will be much easier with more money. Go that route unless you have a passion for creating your own thing.