Actually, it's quite easy.
I tend to maintain "zones" when I unpack. For instance, everything in my suitcase, bag, checked luggage, etc. stays in the general vacinity of where that bag is kept, be it the hotel closet or even a corner of the room. It's not like i repack the bag every time I take something out, I just make sure everything stays near it when I change. My carry on that contains my personal items stays on its table. My electronics stays in the safe if there is one. My toiletries stay in the bathroom. When I buy something on that trip, I make sure it's left in the zone of the bag it will be coming home in.
The point is that you won't lose things if you make it so you don't have to look for them to pack.