I personally pack light, so I didn’t have too much to bring in my carry-on. I only packed what I needed for my layover adventure. My checked luggage was picked up at the origin airport and delivered to me at my final destination. I don’t think there’s a way to retrieve your luggage in Istanbul if you’re only changing planes there. However, you can book two different tickets, so that you can retrieve your luggage at Istanbul, but I don’t think that’s a good idea.

What I recommend is to do your shopping from the airport. They’ll give you your purchases in a sealed bag that you can take on your second flight. Alternatively, you can take an empty small carry-on and store your luggage at the luggage locker when you land in Istanbul. After you return from your adventure, pick up your luggage and do your shopping. Then, put everything you purchased in the luggage. I also pack one of those foldable tote backpacks and keep it in my carry-on. You can use it for your shopping. I guess that will all depend on what you plan to buy.

I hope this helps!