Our research considers the role that new technologies could play in supporting emotional and non-verbal interactions between musicians during co-present music making. To gain a better understanding of the underlying affective and communicative processes that occur during such interactions, we carried out an exploratory study where we collected self-report and continuous behavioural and physiological measures from pairs of improvising drummers. Our analyses revealed interesting relationships between creative decisions and changes in heart rate. Self-reported measures of creativity, engagement, and energy were correlated with body motion; whilst EEG beta-band activity was correlated with self-reported positivity and leadership. Regarding co-visibility, lack of visual contact between musicians had a negative influence on self reported creativity. The number of glances between musicians was positively correlated with rhythmic synchrony, and the average length of glances was correlated with self-reported boredom. Our results indicate that ECG, motion, and glance measurements could be particularly suitable for the investigation of collaborative music making.