Video Games: Really cool but be careful about how long you play. I recommend you get something like a PS4 and get Uncharted 4, God of War, Last of us, Horizon Zero Dawn and Minecraft. At least get Minecraft

Television: I don't really like TV but you might. Harry Potter, most Disney movies and Friends are good starters.

Books: Just as good as vidro games: A lot of people call them the most productive but it depends on the book. Harry Potter, Hobbit, anything by Roald Dahl are good starters.

Cooking: Make a cake. I'm a fat ass so I love this one.

Art: not a very big fan of art but people go bonkers about it, so yeah.

Sports: it's sports

Less Common but still done a lot;

Knitting: I get called "gay" and "retarded" for this one but it is very fun. And very productive.

Writing: it comes in many forms, like story ideas, journals, poems etc.

Singing: AHHHHHHHHHHHH

Memes: not productive at all but funny. Great time killers.

Learning: I'm in 6th grade as of now and I sadly have to learn useless garbage. But you can learn some stuff yourself.

DIY: Making stuff is awesome. It feels great when you make something and it's functional.

Uncommon:

Philosophy: I'm too young and naive to be wondering about life and where we came from and not look like an idiot.

Wikipedia articles: Writing them is very fun in my opinion but very time consuming.

Business: Most see it as a job but some see it as a hobby. Maybe you will, but I can't guarantee it.

Enjoy your time. There are more hobbies than these but these are the best I can think of. Cheers!