What is “fun” and how do you have it?

I’ve been through a lot in the past 5 years and my ex recently told me after she went on a trip to “remember to have fun”.

The trouble is, I equate fun with drinking, smoking weed and having likeminded people do that with me.

Yea, sobriety is on my list of to-dos.

I just don’t know how to do this sober “fun” thing.

Got any ideas? Preferably cheap or free.