I have an Akona scuba suitcase with fin pockets down both sides. My mask and snorkel (only use for snorkeling) go inside with my gear, or in my carry-on luggage.
I have an Akona as well. I puit my fins inside the bag. The fin pockets are alright for transporting in my car. But, the airline baggage chutes are a little too rough for my Mares fins and the fin pockets do not offer much protection. I also usually wrap the bag with Samsonite Luggage straps, like a Christmas present. One strap lenghtwise, the other crossing over widthwise. So, when the airline drops my bag off of a two story building, the bag will not pop open and my SCUBA stuff will not be ingested by some jet engine warming up.
By the way, I bring my logbook and "C" cards in carry on along with my camera and Reg. set. Lost luggage is one thing, lose my "C" cards or my camera / reg. set and my dive trip will be "One to remember".
What Canadian SCUBA said. Take the stuff you can't replace, as carry on, camera, C-cards, computer, stuff like that. For the rest there is usually no charge for a second bag, if it is sport related.