Is there such a thing as an external power pac to use for a canon flash such as a 420EX, something that would attach to a belt or so?
There have been larger external batteries for flash units for years. But what is available today is a question. So I wold first of all check Canon's web site to see if anything is mentioned. The go to Adorama and B&H as they are the most likely sources if such product are made and sold currently. Considering the wedding photography business remains active and is probably a market for large batteries for electronic flash, it may also be a source for information.