I use a spot meter all the time with roll film. I meter the darkest shadow I want detail in, set my exposure, check the brightest highlight and make sure I can fit it in using paper grades. If it doesn't fit, I need to make a choice.....lose a zone or two of highlights or shadows or change the development for that roll. I used to carry an extra back, but honestly, I almost never needed it. I think the zone system for roll film is exposing for the shadows and knowing where the highlights will fall.