Sunscreen is one of the worst enemies of the camera. You should never pack the two of them close together in a bag, but even just by having a little cream on your fingers when handling the camera, you can damage it beyond repair. The oily-greasy stuff gets easily into the crevices of the machine and once it soils the system theres nothing you can do. So wash and wipe your hand between using sunscreen and the camera.
If a camera is digital, that doesnt mean that it hasnt got plenty of sensitive, moving or whirling parts. Neither these parts nor the processors and CMOS or CCD sensors can stand the rough and damaging grains of sand. One easy solution is just not to put the camera in the direct vicinity of sand. With just one tight container or sachet you can prevent any sand damage when using your camera in the desert or on the beach.
Dust can be just as harmful as sand. We shouldnt underestimate its effects because of the small size of the specks, they are big enough to completely wreck a camera. Dust can also insinuate itself where sand cant go, so you should clean your device regularly, and changing the lens of a DSLR camera in a clean dust-free location cannot hurt either.
Water, moisture, vapour
Water is a natural enemy of the camera. It is goes without saying that you should never wash or drop your camera into water. But avoiding water vapour is not so easy. A dangerous situation can arise when you change suddenly your position between two places very different in humidity (e.g. disembarking an aeroplane). One way to protect your device is to keep it in a plastic bag with desiccant in it (the stuff they put also in shoeboxes). You should also wipe your camera time to time when you are in a humid environment.
Salt can get into a camera when a kitchen shooting goes awry, or maybe it happens more frequently when you are taking pictures in a beach. Salt inflicts the same damage as sand and dust, but thanks to its composition it can cause chemical corrosion as well. Remember to wipe your camera often when you are near salt!
Fog & Smoke
Party photographers usually do not like to work in places which are still using oil-based smoke machine, which is very harmful on the long run. More camera-friendly solutions are haze machines or water-based fog generators.