Joint health, bone density, and strength/muscle mass are things you will miss out on if, say, you just play ultimate frisbee. But getting stronger doesnt have to be 3 sets of 8 on bench. You can get essentially the same health benefits by engaging in sports that train strength, like martial arts, acrobatics, or rock climbing. That said, many people who do any kind of physical activity aggressively typically find that they enjoy lifting at some point in their athletic careers, as lifting itself can improve athletic performance and ward off sports injuries, due to the controlled and progressive nature of gym work, as compared to the more chaotic nature of real-world activities.

A commercial gym is not necessary!

So “general activity” I can only assume is stuff like going on walks and hikes, playing sports, enjoying the outdoors, and so on. This will generally fall under the umbrella of cardiovascular exercise which is extremely good, and you should do

Resistance training is typically performed in much shorter bouts of intense activity. It’s very convenient in a gym, but you can do pretty much everything you need with the right setup (bench press is very similar to pushups, for example, which don’t require equipment.)

The biggest challenge outside of a gym is how to progress movements. For example, once you can do 50 pushups, how could you make it harder so that the movement would be appropriately challenging, and not take all day? And then another issue sometimes can be training the muscles of the back without equipment, typically done via pull-ups and rows.

But ultimately everything is doable! Check out the youtube channel “Hybrid Calisthenics”, he’s got a ton of excellent content aimed directly at this question. He also sells cheap gymnastics rings which handily solve the muscles-of-the-back problem, if you have somewhere to hang them from (even a tree!)

Look up calisthenics. You can do it for free with 0 equipment and gravity. Stuff like pushups are under this category. I've been doing it for years