I really had to think about this. Which answers the question. I use my body everyday. It is 30 years old and easily the most used thing each day.
Aside from that, the next oldest item that I use is either my computer mouse or my Nike shoes.
I got my PC mouse in 2012 and my Nikes in 2017. I have two of the same PC mouse. I bought a second one in 2015 only to learn that I didn’t need it yet. So it’s just been hanging out in my desk drawer.
My shoes are falling apart but they are the most comfortable shoes that fit over my leg braces. Sure, they are beginning to come apart, but they are my favorite shoes. I won’t discard them until they rip apart.
I am getting new leg braces tomorrow, and this means new shoes. My six year old shoes will finally retire.