This short video demonstrates how to take your stuff from your old game into your New Game Plus game.
Before starting New Game Plus I take all of my armour and weapons off the display racks at Corvo Bianco and put them into my inventory or stash. If I didn’t do that then they wouldn’t be there when I started playing NG+.
It’s a good idea to properly prepare for NG+ and to make sure you don’t leave anything behind. Anything that isn’t a quest item, and is stored in your inventory or stash (or on Roach), should carry over into your NG+ game.
Note that, after starting NG+, I then skip most of the cut scenes and dialogue to get to the point where I can show my inventory and the items that have carried over. Thus: the choppy nature of the video in places.