DD's team had matching backpack bat bags last year. We made it work, but it was difficult. We got a carabiner clip to attach her catcher's helmet to the outside on one side and she used some of the straps to attach her shin guards on the other side. Once all the straps broke she started looping the shin guards over a bat. I think her helmet and shin guards got more banged up than usual--though it's hard to tell with her. By the end of the season, she was missing two screws from the helmet facemask and one of the straps that attach the knee portion to the lower section of the shin guard had pulled out. Her mitt, fielder's glove, batting helmet and chest protector did all fit inside the bag.
This year her team is going to allow the catchers to pay an upcharge and get a larger wheeled bag
I am of the opinion that the catchers have to bear enough extra costs and in order to "match" the team should be willing to cough up the extra money for the right sized bag for the catchers. Besides wouldn't it just make sense to give a little back to the kids who bear the most bumps and bruises, not to mention the heat.