Thanks , any special Insurance?
For the Tunnel or Boat - Passports are the most likely the docs they are going to ask you for.
For your Holiday in general you'll need what Hovedan has listed above. (Though I personally wouldn't ever take my MOT or V5.). So copies of your Car insurance and Breakdown insurance should be carried. Travel Insurance is you own personal choice.
My advice is to buy Annual Travel Insurance as it's a lot less hassle and generally cheaper and covers you for UK travel as well.