Use a check list to confirm you have everything
Take cell photos of your passport, c-cards and DAN insurance card. Crucial if you lose them and handy if you just need to write down information on entry cards, etc.
Put anything small and expensive in your carry on: computers, lights etc. Pack shears or line cutter in checked bag. Leave knife at home with AK and rocket launcher.
I put my mask in a fin foot pocket. Never had a problem.
Wrap reg in wetsuit and put it in checked bag. On the way home, if gear is still damp it ends up 2 pounds heavier, so I put reg in carryon on way home
Pack lots of favorite snacks, at least half should be somewhat healthy. Great comfort if you need them, good for making friends even if you don't need them.
Bring extra batteries for anything that uses replaceable batteries. You may not be able to find them at your destination, and even if you do they will be more expensive than you can buy them at home.
Download podcasts and videos in case WIFI is sketchy.
Pack modest first aid/pharmacy supplies consistent with your level of hypochondria. Different size band aids for cuts and blisters, antiseptic ointment, anti-diarrhea, advil, favorite decongestant, chapstick, sun block, moisturizer, swimmers ear drops...
Clothing: with 2 quick drying swim suits and 3 rash guards I can do 4/5 dives per day comfortably. Clothing for surface intervals depends on what you have planned and with whom, but a general rule is to lay out the minimum of what you think you need and then pack only half of that.