There are different kinds of fish bags that are made of materials that might be easier to clean when compared to others. Look for a bag that has a non-stick type of interior as this will be much easier to clean as opposed to one that often gets scales, guts, and other fish particles stuck to the inside, making it really tough to clean.  If you find a fish bag that is made with a drain plug that also doubles as a hose hookup, this will make cleaning the bag a breeze that can be done in a few minutes as opposed to having to take the time to scrub and rinse it multiple times.