The easiest way is that you could have made an alternate timeline and that runs simultaneously to the main timeline. This would have a timeline action to restart itself. It could be kicked off by an On Scene Load event.
A similar method is that you could have encapsulated the backpack and its animation in a Symbol, which has its own timelines.
@h_classen also made a javascript library that can make working with Image Sequences easier.
We’re also planning to improve image sequence workflows in the next version :).