Depending on the age and genre of the film, 'spunk' could be a coarse reference to semen or a reference to a person's courage.
My impression is that the courage type usage is becoming obsolete.
I think it's still describing cum...
Not that I've heard anyone use the phrase for quite some time, but would the phrase not be something along the lines of 'he's got spunk, that boy'? In the same way that you might describe someone as 'having balls'?