We've have a couple of normal sized gym bags in our time and always felt they were too big for every day training.
The Zido Classic Bag is designed to be large enough to carry what you need for training/the gym/and during the day.
It has a main compartment which is double lined and keeps out water (we tested this when we accidentally emptied a half closed drink bottle on top of the bag) and a side compartment which isn't lined but prevents the need to rummage through the whole bag for things like keys.
However it's small enough that you can ride public transport without hitting people on either side of the aisle.
It also is the perfect size for carry on luggage on a plane.