What do you carry when you're not supposed to?

Last week, a client handed me a thermos after the climb. Said it was for the descent—cold tea, he said. I didn’t open it. When we reached base, I still had it in my pack. Not because I forgot. Because I didn’t want to know what it was. Now I keep it on my shelf. It’s just a thermos. But some things aren’t empty. What’s something you’ve kept that wasn’t yours to hold?