Interplay is something which seems helpful at making me more spontaneous. Interplay is hard to describe, but it has aspects of meditation, dance, yoga and improv.
A description from SF Interplay site:
Learn to have more ease and openness through improvised movement, story, voice and stillness. The spiritual practice of InterPlay can facilitate deeper connections with the divine, other people and our planet. As improvisation becomes easier in our bodies, we have more access to our own wisdom, making us less afraid of what might cross our path. Rather than reacting with fear and paralysis in the face of what is unknown, we can breathe, dance, and find fullness.