Pack your charger and/or spare batteries somewhere you can easily reach. If you are driving on your holiday a car charger can be useful. Remember that using a flash, high speed multi shots and previewing your images all use up more than normal battery life. Batteries don't last as long in cold weather.
Check that you have a nice big memory card, and carry a spare. there is nothing worse than having to delete photos because you have no more room to save new ones. If you are taking lots of snapshots set your camera to take slightly lower quality pictures - this will save you a fair bit of memory.
Back up your photos when you can, to a separate hard drive or to the cloud if possible. This way if you lose your luggage or drop your camera in a river most of your photos are safe. An easy way of doing this if you are using your phone camera is to automatically upload photos to your Facebook account every time you get to a Wi-Fi point.
Preview your pictures often to ensure that your camera is working as it should. Take lots of photos!! Even if you think you are a bit far away from the subject most cameras are good enough quality to allow for cropping in post production software when you get home.
Don’t be scared of using the automatic settings on your camera. Modern camera’s are pretty smart and can make sense of all sorts of tricky light situations, saving you the drama of mis-calculating f stops and shutter speeds and wrecking that one opportunity of photographing your loved one bungee jump off a bridge …
Please please think of your personal safety. Don't take pictures from the middle of a busy road, stop your car on blind corners, climb over safety barriers or go for walks without taking basic safety precautions and some warm clothes. Every year tourists get injured and killed in New Zealand doing these things and the tragedies are easily preventable.
A handy tip for getting rid of blue haze, making clouds more dramatic and seeing into water is to use a polarizing filter. If you don't have one a polarized sunglass lens held in front of the camera will do the same job.
Lastly a tip I learnt from bitter personal experience - never pull your memory card out of the computer without first ejecting it properly. In my jet lagged haze I did this after Nairn and I returned home from a holiday in Rarotonga and destroyed most of our photos, plus the memory card itself. A stupid, expensive lesson!!