I'm not exactly a theist, but I consider myself spiritual, so I'll take a shot at it.
To me, spirituality is having a connection to something bigger than yourself, beyond your own ego. Eastern philosophy appeals to me in this regard, as it points to transcending your ego/self. IMO, spirituality is primarily an internal affair, what the Gnostics called "gnosis". Gnosis refers to enlightenment, rather than knowledge. Unlike rational knowledge, putting this state into words is difficult - as the Taoists put it, "the way" is beyond words, it is experiential. I often feel this way in nature, this "connectedness" - which causes me to relate to pantheism as well.
Spirituality ISN'T "works" and doctrine. One of the problems I always had with the witnesses is that they associated spirituality with mundane tasks like meetings, service, etc. To me, spirituality is about transcending these petty, ordinary tasks.
Spirituality isn't a laundry list.