What are some things my fellow friends and I can invest in to ideally create a second flow of cash aside from our main jobs?

Most of us are recent graduates (22-24yrs old) and making over 100k. We invest separately a bit in some index funds. But is there anything else that we should allocate some of our money to that could potentially bring about a lot of wealth long term?

I’m aware this question is very broad and doesn’t have a “right” answer but just looking for some ideas.

We have been considering getting into owning rental properties but that is just one idea.

It does not just have to be investing in stocks, even business ideas that would be profitable in 2026+.

Just looking to take advantage of our position right now since we did not come from generational or inherited wealth