1. Free food.
Many organizations have call-out meetings and events where food is provided. Why cook for yourself when you can go to a fun club meeting and eat free pizza?
2. Leadership skills.
In a lot of organizations, you can run or apply for leadership positions. This will teach you valuable skills that you can use in the real world.
3. New friends.
Friends are fun. 
4. Discover your passions and strengths.
College is the time to figure out what you want to be in the world. Joining clubs that interest you is how you learn more about yourself.
5. Adds more to the Class-Home/Dorm Room cycle.
6. Awesome resume.
Being in various organizations, especially those that pertain to your major, looks good on a resume because it shows you can manage to get good grades and be involved.
7. Learn skills that aren’t taught in a classroom.
8. Networking.
Through organizations, you will meet various faculty and staff at your university who could write you letters of recommendation or point you toward great opportunities. 
9. (Sometimes free) T-shirts.
If not for the free food, do it for the free T-shirt.
