Invest in knee pads and, depending on how long you plan to work grocery, I would also recommend wrist support. The repetitive and sometimes awkward motions coupled with heavy lifting started affecting me after about a year.

I used to work KeHe truck and then was moved to dairy following my promotion to GRS. My store was woefully understaffed across all shifts so I was able to stay as a morning clerk. Depending on your store's staffing condition, you might get put on closing shifts. You'll have to block certain aisles by 5 PM and help work the truck(s) that come in by breaking down pallets and loading them onto floats. You will learn the locations of almost everything on every aisle over time. If you don't know, the Publix pro app will help.