We have used SolidWorks for 90% of our packaging work, and complement that with Rhino for the oddball needs. Granted we do a fair amount of blow-molded structures so those need to be done in 3D for proper design intent translation, and simpler packages could be done in sketches or ideally AI. I believe most retail-type design use 3DS Max or even FormZ.
Ditto using the sheet metal module in SW as a substitute for paper.