What you see there is part of the jetpack's working exhaust system. It has a metal tip connected to a flexible tube which was then connected to a pressure tank (intentionally put upside down) and when it was activated it released air (or gas) in fog or vapor form:
All the jetpacks shows this particularity with some minor differences, especially at the Supertrooper/Pre-Pro #1/Pre-Pro #3 it seems like missing or it is another variant.
It's hard to tell if that is a found part or a custom made object, but anything is possible.