Just say thank you for delivering my "personal products"
that should do it. It's all in how you say it, and if you are or are not able to say it in such a way as to make the person smile. If they are nosy, just re-direct the conversation geez.
Make 'em smile. What else counts? Hear the new study that saying "I'm sorry" (when an apology is called for) actually
induces improved physical feelings/functioning? By the same token, making people smile does about the same thing.
It's just really a matter of how much you care. I show my regard for my mail carrier by keeping the mailbox lubricated, dry, easy to open and shut, keep the flag easy to retract and sanded down so fingers can't get cut. Put yourself in their shoes - that's empathy: one of the greatest virtues IMO.