I occasionally run commute, taking pubic transportation or getting dropped off at work and then running to the public transport station. I started with a Gregory Miwok 18, but that ended up being a little too big for my liking since I realized running with dress shoes on your back is no fun! It's actually a great pack, just bulkier than what my stride likes.
https://www.gregorypacks.com/day-hiking/active-trail/miwok-18/68380XXXX.html
I've since switched to the Salomon S Lab Sense Ultra 8 Set Hydration Pack Vest. Got it for just over $100 on eBay. It's great! It has just enough room for the essentials and doesn't make me feel like I'm running with a pack. I use it to keep my phone, Gu and/or chews, gloves/beanie (if necessary), and some wipes and an extra pair of longer shorts so I don't smell like balls and have short-ass shorts on public transportation when I'm done.
https://www.salomon.com/int/product/s-lab-sense-ultra-8-set.html
Hope you find the right pack for you! It's hard to know until you've actually bought it and run with stuff in it. That Miwok cost way too many hours of research and almost $100. Now it's pretty much another bag in my closet that is rarely used.