I mean, if you want an answer to that you could just stop using your smartphone for a few weeks and see what your brain comes up with. Here's a short list of some examples that were popular when I was a kid and smartphones did not exist yet:

Magazines, the daily newspaper, books, going out and exploring, shopping at malls, doing a hobby or craft, personal projects, television, chit-chatting with friends or even strangers, video games, puzzles, play with your pets, exercise, play sports, sitting quietly and being alone with your thoughts.