People come in all shapes and sizes. Sometimes we are too short to reach the item on the top shelf, and sometimes we are too tall or inflexible to reach the items on the bottom shelf. The next time you are shopping take notice of the other shoppers around you. Is someone having difficultly reaching an item? Help them.
Is there a random cart obstructing a fellow shopper? Help find the owner and move it. If you frequent a specific store often, you can even help others find certain items that might be eluding them. Simply be aware of those around you and offer to help if needed.