When I cruised on the Carnival Legend two months ago, we were required to carry the lifevests to the Muster Station during the Muster Drill. However, we did not have to put them on. And we just stood around and watched the crew member demonstrate how to put one on.
I suppose they wanted us to carry them, just so the crew members in the bright day-glow green baseball hats could point the passengers in the right direction (by seeing the number on the lifevest). The only problem with just carrying them to the Muster station was that the strap would drag on the ground creating a trip hazard.