I carry my camera and strobes, along with the myriad of wires, battery chargers, additional lenses, etc, etc, in a pelican wheeled carry-on bag, and it always used to get attention from the screeners. However, on this last trip to Cozumel a week ago, it sailed right through screening without even a glance! But, the Mexican screeners looked through our other carryon stuff, and confiscated an unopened package of AA batteries and a partially used tube of toothpaste in a bag. (!) They have gotten hinky about batteries before, but a quarter tube of toothpaste?
We always manage to have some kind of fun with the Cozumel screeners. We each also carry a backpack with basic scuba gear and clothing in it, and have never had problems with this. I must admit, it is a comfort to know that your reg/mask/computer etc. is safe and right there with you on your trip. I have been lucky with my checked baggage (so far) but many others have come to grief, so a little foresight does not go amiss, I think.
If it is something you cannot easily rent or replace, carry it on with you. Schlepping stuff through airports (and you can streamline this considerably with intelligent packing) is a small price to pay for having what you need when you get there.