Arkel Commuter

Has a suspended laptop pouch, latching rack attachment which is adjustable for fore/aft location and comes off with a pull on one handle, has super-tough fabric, is water resistant, and you can get a fitted rain cover for down pours. Just big enough for laptop, lock, rain clothes, warm cycling clothes, work clothes and a few other random things.

I also have a 4-year next business day on-site service contract which I expect to use (I went through three main boards, one screen, and one hard drive in three years with my last Dell commuting with a back pack).

If your software needs are compatible, your files on a thumb drive or virtual machine on a USB hard drive would be easier to accommodate. Mine aren't.