Crikey, I confess myself to be somewhat gobsmacked by the list of 'essentials' some forumites have included!
I have just returned from a 9-night stay at the Blackmore C&CC site. During the very cold spell the site suffered numerous black-outs; I can't help but wonder whether all these electrical goodies that have been suggested were all given heavy use during the dark, cold evenings. E.g., most of the black-outs occurred at mealtimes, so were there lots of these electric hobs in use, as well as toasters, televisions, microwaves etc? And of course most people would be powering their heating via the EHU as well?
Quite apart from the consumption of power, I'd be concerned about the additional weight of all these 'essentials', one always has to bear the loading allowance in mind. DJMilly, when you get your caravan, and start accumulating accessories for it, it might be an idea to weigh everything to ensure you don't exceed the maximum for your caravan.
Lots of advice has already been proffered about the two major clubs, I would certainly advise you to join one of them. Quite apart from the advice you get via this forum, both clubs offer help and advice on all aspects of caravanning. Added to which you will receive details of all their big sites (all of which are to a certain standard, which I consider clean, secure and quiet!) plus a cornucopia of smaller and often more basic sites, for members only.
As Emmerson says - go out there and enjoy yourselves! Don't stock up with too much stuff to start with - you will learn by experience what is going to be appropriate for you. Good luck, and happy caravanning!