I've posted before that I have a bunch of "active" sketchbooks at any one time. Currently I'm rocking two in my backpack - one large one & one pocket-sized - two others that I bring to life drawing and one in my car. On top of those five, I have my wallet, which is a Moleskine notebook, money & credit cards slipped into its inner pocket. I've been using Moleskines as wallets for years, well before I started drawing daily again. Before everyone, including me, had smartphones, I had a little notebook with me at all times, back then filled with phone numbers and addresses and random notes. Now, it's for quick "standing in line" sketches and random downtimes when I didn't remember one of my other sketchbooks.
Here be a smattering of sketches from my current wallet.