It's very important to have common activities, but there's sooo many fun things to do out there...if you have none obviously in common you can always try new things and see what you like.
With my bf I play volleyball and soccer and we like watching some of the same tv shows and movies. We both like hiking and camping and stuff like that. There's probably other things that we don't do often,too. Nothing particularly fancy though, by any means. Most of our time "together" is us each doing our own thing in the same room, typical of introverts.