Yep, pen and paper.
It's just a simple notebook.
I know many people find success logging food, but I know from experience it creates a very unhealthy fixation for me. It feels like I'm tracking the bad. I spent a couple years obsessing over food, limiting it, etc, and I try to avoid anything that leads me in that direction. So, by tracking activity, I'm logging the good things I do for my body every day instead, which is much better for me.
How are you keeping yourself accountable? I've seen others post some cute fitness journals and such, but having missed 2 classes due to the snowstorm, and having missed 4 classes because the gym had holiday hours, I'm trying to be frugal, so an el cheapo notebook it is.
Speaking of snowstorm, did you get hit? We had twelve inches total officially. And I kept our driveway clear. Just call me a snow beast.