I pack the same for myself as I do with my wife, we have nearly identical suitcases.
I happen to use a 29" Travelpro Maxlite spinner. It weighs just over 8 lbs, leaving at least 40 lbs for packing. I have never had a problem staying under the 50 pound limit. I pack my fins, mask, BC, wetsuit for conditions, hooded vest, booties, mesh backpack, and accessories (light(s), cutting, gloves...). In addition, I pack the majority of my clothes. There's always room left over for other stuff, coat, raincoat, etc.
I pack regs, computer, camera, toiletries, swimsuit, some clothes, and all personal items in a small, light spinner carryon and a backpack. On occasion, I have arrived without my main suitcase and do fine for a day. The backpack generally gets use after arrival.
I use a digital luggage scale to check the weight of my main back, my carryon, when needed, or my total luggage weight. This has saved me aggravation.
How big is the backpack if you also take a spinner carry-on (rollaboard)? I assume it is small enough to be considered a mere "personal item," like a briefcase or ladies handbag? I used to put regs in one of those dedicated regulator bags and take the position that that was my personal item, but I soon found that too annoying. Now I carry on only one bag, generally a medium-sized backpack.