Are usually the ones that are overlooked.
I used to constantly forget my reusable grocery bags at home when I'd unexpectedly run to the grocery store (lets get real, even when I expectantly go to the store I forget). So I took some advice from my M-I-L... leave them in the car! Done - they sit in my trunk.
Yes, I've walked into the store and forgotten them, but usually realize at some point. I then run out and grab them leaving my filled cart in an aisle out of the way waiting for me. It works - we take home far less garbage and use far less plastic. Easy Peasy.
I forget my stop & shop card when I get gas all the time... so I took the card (the one that's not a key chain) and leave it in the car 24/7. We only have 1 car and if that gets us the occasional 10 cents off a gallon... it's WELL worth it.
Now I have no clue why but it took me stepping into the store without my stop & shop/CVS/ETC card approx. 5-6 times before realizing my key chain of discount coupon cards SHOULD go in the car along with my reusable bags. Duh! Like seriously what was I thinking. In NY I used to have them on my house keys, but I find that it's too big now. So I have them all on 1 key chain attached to my bags via a carebiner. And now ... they are there, waiting to be scanned along with my bags. Easy peasy!
So now I can shake my head and say... "DUH!"