I would second Robin's suggestions - avoid using compressed air on lenses to remove sand or dust as you're more likely to blow it in, use a brush instead. I use air on the front element in my workshop, but it's filtered compressor air (not canned air that can leave residue) and I'm careful not to have it too strong. I use a brush on the lens body. If sand gets under a lens ring and the lens starts sounding crunchy it needs to be partially dismantled by a technician for cleaning.
Don't Vaseline anything, you don't want sticky surfaces in sandy or dusty environments. Bag things as Robin said, try to do mag and lens changes in a truck or protected space, wipe everything down meticulously at the end of each day. Be extra careful when it's windy. If you see screw heads or external metal areas beginning to whiten or tarnish due to corrosion use a rust inhibitor (I use CRC 2-26) on a cotton bud to clean the area. A dab on connector pins then worked into the socket will help avoid electrical issues.
If you drop something in seawater submerge it as quickly as possible in a bucket of freshwater and send it straight to a technician.
If it's rental house gear you can ask them during prep what they recommend to protect their equipment. Corroded or sand damaged gear will attract a hefty repair bill when you return it.