However much of a record you make of your journey there are a few basics that are best thought about before you set off.
The first thing to think about is how you are going to record it. These days many people will automatically figure to use their smart-phone, as they go along. This is certainly a valid possibility, but one which does have some drawbacks. How often do you need to charge it? Are you always going to be able to find somewhere to do so? How vulnerable is it to being dropped or getting wet? It can be a target for pickpockets. How easy is it to transfer to a computer upon your return? Is it going to be easy to structure the information as you record it? On the photographic side, will the pictures have a high enough resolution? 300 dpi is needed for professional printing (See page 32). Quality can also be an issue with sound and video.
Personally, I believe in the good old-fashioned sketchbook/journal as the primary record. It is pretty rugged and is not likely to get nicked. It can be well supported by a smart-phone or a tablet, camera and even a solid state or mini-disc recorder.
I see the record of a journey or adventure as a kind of layer cake. The number of layers you put down is your choice, but you always need the bottom layer, - the facts, the objective reality.