I have a generic leather backpack with a design similar to this one. It's a decent (medium) size and can fit everything I usually want to have with me: iPad and/or laptop, snacks, chargers, toys.

I like the small pockets on the front for accessories, the side pockets are just large enough to fit a water bottle, it has a top handle, and the leather has worn very well over the years.

I am not a fan of the thin fabric lining (including the slightly-padded computer pockets) that sags away from the sides. The outside pockets were just tab enclosures until I added actual buckles and straps (I found leather dog collars that matched the bag leather). The shoulder straps are narrow, so I made wider leather pads to go over them. I also added some dense foam to line the bottom, as I didn't trust it to protect electronics.

Once modified it's done everything I need, and I've had it on many trips with no issues. Plus, the design gets at least one positive comment every trip.