Your dive gear might be given the bomb-swab. They take a sterile swab and touch all your items looking for traces of explosives and narcotics and the like.
Best thing to do is explain it calmly, don't sweat and revert to citing religious phrases to keep you calm.
You're also good for a full blown carry-on. You can take what you're taking now and a laptop if you like. It's 2 items, one carry on and one personal item. The personal item just needs to fit in the seat in front of you (I like to take an item with a strap so I can keep it looped around my foot). Usually I will have my red flight bag with flight gear (I ALWAYS get the thorough frisking and prodding when I take my headset...annoying) and a backpack with a change of clothes and my computer. Soda, gum, skittles and what not as well.