What is the 1 item you brought with you on a backpacking trip (most likely early on in your hiking career) that when you got back home thought to yourself "What in the HECK was I thinking?"

I am sad to say that mine was a battery operated fan. The fan itself was lightweight, only 6 ounces. I think it might have been the 4 D batteries that caused the issue! What can I say, I'm a picky sleeper...