I used a backpack for a short while and hated it. Rack and trunk bag/panniers are WAY better!

But I also leave quite a bit at work. Towel, wash sponge, body wash (that's all I need for showering) all stay at work. Duffel bag for carrying clothes back and forth to the shower stays at work. Shoes stay at work. The only thing I carry on my bike are the clothes for the day, and lunch unless I brought the lunch for that day on a previous day or I have other lunch plans. Makes commuting easy peasy. But I also don't carry a laptop around. That would make things a bit more difficult. I'd probably have to use regular panniers instead of my trunk bag's fold-out panniers.