Regardless - don't check anything you aren't prepared to say goodbye to.
https://www.southwest.com/help/accessible-travel-assistance/...
But also I've traveled for a month (us to India) from my backpack. One week of clothes, a laptop, some cables, notebook and pens, perhaps a couple more books, a few toiletries. And still some room for one 'fun' thing, like a small synthesizer to jam on.
It's a bit like ultralight backpacking; you can cut down quite a lot one you get in the mindset. I definitely don't claim it works for everyone... But probably most people can travel rather lighter than they normally do.
Fwiw, my travel backpack is pretty similar to this one. Definitely a bit bigger than the standard backpack, much smaller than a hiking backpack, and rather smaller than a roller bag.
https://www.chromeindustries.com/product/hondo-backpack/BG-2...
And usually not in a city other than your point of departure or expected arrival.
Southwest should be responsible for making it worse.
Keep it on your person. Always.