How do I link them so that it won't be like a list of activities? How do I even start?
Great question! You need to be creative, and you need to have seen lots of great pieces of writing so that you have good ideas. Your ability to do this in an impressive way can set you apart from the others. So... without giving an idea that would be MY idea instead of your idea, I'll tell you the secret key to this sort of dilemma:
Use a theme.
One essay = one big idea
If you think about all your activities and your chosen field of study, what theme comes to mind? Whatever it is, write an insightful piece of writing about the significance of these activities, these components of the life with this particular theme.
The theme is the glue that sticks them together and points them all in the same direction.