I got my extra heads separately because I found them individually over the course of a few months. The cardboard insert that they come with in the box makes for a perfectly serviceable method of keeping them from flopping around inside a systainer. By the same token, a few pieces of cardboard or plastic or fiberboard or even Kaizen or pick-n-pluck foam would do the trick just the same. And then you could use a T-Loc instead of a Classic.
Or even a pull-out storage drawer, [member=65062]DynaGlide[/member] style:
https://www.festoolownersgroup.com/festool-tools-accessories/sys-vac-question/msg584005/#msg584005