I wouldn't try to carry my fins; too long, but your's may be shorter.
I do carry almost everything I can in two pieces:
(1) a rolling bag that will fit in the overhead of regular jets, but has to be gate-checked on commuters and regionals. I usually get it right back when I walk off the plane.
In it, I'll carry clothes, swim suit & flipflops, and personal stuff i'd need for the first 24 hours, if my checked luggage didn't make it, plus my computers, my octo-reg, my prescription mask, and anything else I can get in there. I also carry photocopies of my passport, travelrs checks, and all IDs.
(2) a small backpack, that passes as a "laptop bag" with medicines, papers, passport, real travelers checks, and no one else ever gets this bag! I'll stick everything I normally carry in my pockets in this bag for easy screening and good control of lose itmes.
Additionally, I'll carry 3 credit cards - one in each carryon plus one in luggage. And I'll clean my nails at the airport, then stick my pocketknife in my dive bag.
don