Hiking, cooking together, playing board games, card games, playing music together, exploring, and just talking are all inexpensive or free. The most interesting people I've known in my life focused on those things anyway.
But more importantly they require time away from working/studying/optimizing for bank account balance.
Again, this is more about choice rather than necessity. Carries a different vibe if you're trying to do whatever you can reasonably afford, and that may mean not spending anything extra. Good friends will accommodate, but if it's obvious you're making over 100k a year (without significant dependents etc.) and won't split gas, well that doesn't lend itself well to collaborative fun times.
Edit: Also, I don't mean to suggest saving money in general is inherently bad. Obviously not. But you need to be able to find that balance. I personally tend to place higher value on the chance to hang out or have a drink than having 20 more dollars in the bank. But many drinks over many weekends maybe not as much.
Of course if you value your time more than what your employer is paying you then you either need to leave your current job or rethink what's the value of your time.
There's many different kinds of people on this site.