My phone. I know it's boring but it's the thing I never go without.
I was the first kid on the block with a cell phone. It was 1991 and it was huge and heavy. I sure knew whether it was in my purse or not.
I've had a few new ones since then.
Right now I have 2. One for work, and one for me.
I take mine everywhere. Just in case.
I live not quite in the country but almost. And I take it in case I get stranded. It's a safety thing for me. It's less about always being able to chat with my friends or family, and more about being able to call for help if I have car problems.
And my Dominant likes to be able to reach me, so I take it for him.
And I run, so I've called for a rescue a couple of times, and a couple of times just cause I couldn't make it home again..
I didn't always take it running. When you run, you want to run light if you can. My husband used to nag me to take it, and sometimes I would, and sometimes I wouldn't.
Once I was training for a half marathon. Training was going well, it was several weeks before the race and I was doing a long practice run. It was cold and damp, kind of crummy but the run was going well. At about 15 kilometres I slipped, twisted my ankle, badly, and fell by the side of the road, onto the shoulder rather than the busy highway thank goodness. I called home to say I had hurt myself and to tell them where I was. My rescuers were there in about 10 minutes to drive me home and ice my ankle, which was about the size of a grapefruit by the time I got home. Which prevented me from running the darn thing, or running at all for about 6 months btw.
So when I'm tempted to go without I think of that day and almost always take it. Though occasionally, very occasionally, If I only go out for 20 minutes, I'll live on the edge and go without.