There’s several applications for packrafts. Some obviously require the burliest rescue equipment, with all the government approvals.
Assuming we’re not talking about that here, what’s left are simple crossings to facilitate a planned backpacking route, lake hopping, short stretches of class I-II rivers, etc. Typically one would bring a bulky white water vest of the most minimal design, but this is obviously not in the spirit of minimalist packing. In some instances no flotation vest at all might well be the route, in other scenarios an unapproved snorkeling thingy is all it takes.
It boils down personal comfort and risk taking, plus land administrators and their rules (and one’s willingness to obey!)
I do 90% of my packrafting adventurers on southwest rivers. Besides the obvious biggies, most have minimal flow when one happens to have time off. On both the Dirty Devil and the Escalante we went without PFD’s and didn’t feel unsafe. This include my kid, and my feelings as a parent.
Because of strict regulations in Canyonlands (which affords incredible backpacking loops using packrafts on class I), I mostly bring the real stuff. In winter, when lack of patroling could tempt one to forego the rules, the water is cold enough for one to feel sketchy with sub-standard gear.