Good advice always has its exceptions. But in general you should never use a work device for personal use because it’s very easy for that information to be either compromised and/or used against you.

My personal guidance is “if you don’t own the device, pretend the owner is looking over your shoulder” it’s incredibly easy for them to install keyloggers and trackers remotely and silently.

It may depend on the store. My local publix trains it’s employees like Chick-fil-A does, and they probably would be offended if you didn’t let them help you.

The baggers at my local food lion (if there is a single one in the store) are offended that they have to help you at all (probably because they’re expecting you to be the fifth person today to come back in the store demanding a refund for the one cracked egg in their dozen)