For me, having a laptop is the flexibility that allows me to choose whether or not to ride or when to ride. I log my hours and get paid for any time I work off the clock.
My pannier is a cheap thing I bought from Target on clearance a few years ago. It has a strap on top and lifts off the rack so I can take it with me.
IMO the backpack is the most useful. My commute is about an hour each way, that’s kind of a long time to have that much weight on the back.
My work commute is 90% on open roads out in the countryside, long stretches without stops and usually quite windy. The pannier definitely has some serious wind drag. But in town, with a bunch of stops,
etc, drag is not a factor. I appreciate being able to sometimes take the pannier and my backpack to the store, I can get 2 full bags of groceries in each the pannier and my backpack and strap a full paper sack to the top of the rack. But that’s a only a 2 mile ride.