We all multitask, or attempt to. This idea of multitasking is a bit finer as it attempts to utilize your idle body parts.
Imagine you grab a bag of cheese out of the refrigerator and are walking to your stove to put cheese on some food. Instead of opening the bag of cheese when you arrive, you can open it during your walk. This makes use of both your legs and your arms.
If you can apply this daily and save 2 seconds, that adds up to ~10 hours in your lifetime. Suppose you find ~5 of these useful, that can be 50 hours of savings.
I look at this list and admittedly they seem a bit trivial or obvious, but I went for breadth in order to give a plethora of ideas.
I partially want to apologize about how simple some of these are. I hope the greater takeaway is a new consideration of using your hands and mind while walking. These are merely ideas to consider in the future that can save you literal days of your life in efficiency gains.