So just having one activity in common would be enough? What if you started out having a mutual enjoyment of a particular activity, but over time, for various reasons, one of you no longer enjoyed it? If you build a relationship on shared interests, and one or both of you change your interests over time and they no longer intersect, what then?
When that happens I always try to figure out something to do...or something new to try. Like hey, would you like to go for a walk or bike ride in the park? Maybe go ride some horses? Play some pool? Pick out something we can cook together? Doesn't have to be the same activity all the time, just so long as there is one.
With my oldest ISTP friend, we lifted weights at lunch almost everyday for about three years. Played golf every other weekend. Eventually my job location changed, but we'd always encourage each other with getting back into weights or running...after months of individually loosing "sustained effort" over the years.
After five years we were both tired of golf. Got into dirt bikes and motorcross, would meet up to play pool on a weeknight about every other week. He and his wife moved to another city, and it's kind of funny I'm wanting to play golf again...and he's been thinking recently about getting back out there too.
Other activities we'd done over time: Water-skiing, tubing, swimming, biking, hiking, bowling, sports event, concert, building PC's, swing sets, remodling projects, helping each other move, car repairs, car shows, video games, drinking more than a few beers, double dating, playing guitar, talking about/listening to music, grilling out, chillin' at a bar, watching "Fight Club", getting pissed as hell at each other and arguing. :steam:
After my friend got married, he was always looking for activities to share with his wife. Bought them both bikes. Later a little golf. Bought her a dirt bike. Those interest didn't seem to sustain for very long? Like she'd come along with us a time or two, but some of the activities just didn't seem to be a good fit for what she liked to do? I thought it was awesome that she would try, and did amazingly well with a dirt bike. Just wasn't her thing.
So I think the variety of things she's willing to try, in addition to what they go do...keeps him happy.
Most of my other friends, there'd usually only be one or two activities shared in common max. Only the STP's whether E or I seemed more ready to go and do. Or maybe "click" enough to get the common activity/interest sequence started.