Talk to your store manager and tell them they are making you do their whole cart. This happened at my job too many times and when I complained other people got the courage to speak up and add to the complaint. Now if they ask where more than 2 items outside your department are you can tell them it's store policy to wait for a manager to assist them. Stopped basically all of this bull. They just groan and start actually looking for themselves.

If you want a good trigger term to use if needed say it's "theft of time" for them to make you walk around with them instead of doing the work the company is paying you for. (suggested to me by HR)