We need to start thinking about images a long time before we go for holiday. First of all, knowing where and when we go, we need to rethink the equipment, which we intend to take. When you want to spend two weeks in Egypt on the Red Sea and you intend to spend most of this time in warm seas, probably you will need underwater housing, as well as a way of securing equipment from sand on the beach. However, if you are preparing for a week trekking through the mountains, a key element will be the comfortable bag in which you will pack your photographic equipment, while the tent, food, clothing and camping equipment will be put in the backpack.
It is worth making a list of things that you need, and then see what you already have, and what you need to buy. Think hard and do not take with you unnecessary things. On the other hand, you would be sorry if the lack of a specific gadget ruined your photo opportunity.
If you plan to stay in a developed country, you do not need a large supply of batteries. When we take into account the lack of power in some places during trip then that you need to have lots of spare batteries.
Supply of memory for storing photos is another thing to consider. Capacity of memory cards is rising, and prices are falling, but if someone just bought a brand new 10-megapixel SLR, that each photo will use lots of space. Buying a memory card with big capacity is a major expense. The alternative is to have reserve flash cards sufficient for 1-2 days of photographing and then you can archive data on your computer. You can also burn your photos on CD in internet cafes, but that way you risk losing your images - we can not verify that they were well recorded.
The last thing on your list which you should consider buying is convenient backpack or bag for camera equipment. Which of these accessories you choose depends on your preferences. But remember that the bag which is comfortable for walking in the nearby park does not necessarily proves to be good for full day of hiking. You may find that in addition to camera equipment you need to pack water, sandwiches and a warm change of clothes. It's better to choose a bag which will have a spare room for extra stuff, not necessarily only photographic accessories.
Do not wait with purchases until the last moment before departure. Do this to avoid the rush and overpaying. You should avoid taking equipment which you never tested before - even the best camera made by the most reputable company can break down in the first two or three weeks - this may be the effect of shipping damage or manufacturing defect. It happens sometimes. Avoid such surprises by buying equipment in a timely manner. If you have time try to learn how to handle new equipment, which increases the chances for successful photos.