Would it work to exhale hits into a plastic bag to prevent wasting good product? I mean your lungs cant absorb all the hit before you need to exhale. Are there any disadvantages to this?

The vapor rapidly crystallizes as it cools. If you go back for it quickly or pass the bag & theres alot in there it may work. Aside from that it'll just condense & be impossible to get back from the bag.

....As he slowly exhaled the third hit into a 2L beaker, hoping to recycle the vapor for later re-crystalisation he was struck; not by anything physical, but by a strange sense that he was in the smoke. Slowly being extruded into the glass beaker. ....