How to write a very good curriculum vitae for a summer school application?
There are few tips I can give, I am in no sense an expert on CV preperation. I just recently prepared a few. Most important thing to remember is the reviewer most likely is going to or has already reviewed more than a 100 applications and CVs. You are playing the game of attention grabbing. Reviewers will skim over papers and most likely won't go in detail of each application. Your first aim is to catch their attention and direct this very limited attention to the most important aspects of your application. If you can manage that, your application is much more likely to be read in some detail. Here are few tips.


Keep it tidy and readable. not to many titles, colors or even fonts. It should be designed minimalistically. 
Use LaTeX to prepare it. It helps explain your proficeny in LaTeX. It is also is easier to update and maintain.
Make each bit of information concise, highlighting important points but also further information should be accessable easily. I personally like hyperlinks but in most cases date, name of the program and name of the institution would be enough. 
Don't let less important stuff to grab attention. Assume someone will only glace over it. You need your best achievements to be "the hook". If their eye catches more important deeds like a summer project then they will read it in detail. My personal preference is to put more relevant bits of information up top, add few lines of details to make a quasi-block of information that is likely to catch attention. I also prefer to "underexplain" some less relevant aspects so that the important bits are seen first. Let me try and illustrate what I mean.


This would be the important bit.


whereas this would be the less important bit. 



Don't let the unimportant or less important stuff to take up space. Keep in mind, you always want to highlight your most important achievements. If you spend the same amount of space for your hobies or coding skills the reader might get disfocused or plain bored. If you wish you can put a Github link or name an achievement or two relating to your hobbies but they really should not overtake the readers attention.