In my suburban high school social world, before cell phones:
- Loitering around shopping malls
- Showing up to the movie theater an hour or two before the movie we all agreed to watch together, and then an hour or two after.
- Parks and playgrounds if the weather was ok
- Cafes, diners, restaurants where lingering was tolerated, even for those who didn't order anything.
- Local sporting events (usually high school or rec league teams).
A lot of these still exist in some degree, but the loss of malls and movie theaters has really put a damper on things, and the rise of cell phones has deemphasized the need for in person interactions with peers (rather than following an influencer on social media).