When driving abroad, you'll always need the following:
- A valid driving license
- Your vehicle's registration document (V5c)
- Proof of car insurance
Some countries have different driving requirements and regulations, so it's best to check local government websites before you travel to make sure you have everything you need to comply with the local laws. Googling 'Driving abroad in the country you're travelling to' will give you links to the best resources for the information you need.
If you're planning to take a rental car on a ferry, you should check with the rental company before you travel to see if they allow this and if there are any extra requirements they have for taking the car abroad.