Katja, it is a bit funny but it works for me. I travel with 3 things to look after on flights and it doesn't matter if I've already checked a bag.
My small purse
My small carry on bag
My jacket
So I count to 3 a lot. Has worked for me for a long time.
When I check out of a hotel, I'm wearing my jacket, so I'm back to 3 again:
My small purse
My bag to be checked
My small carry on
I am amazed at how many folks loose stuff when traveling.
Keeping up with a scarf/Sholdit would make item #4 and there is where my system might fail.