We had a mobile home last year on a Haven/Siblu resort in Brittany. It was very well equipped in the kitchen and the only things lacking would be if you wanted to do a lot in the oven.
They provided good duvets which kept us warm enough at night, plus the van did have heating (mains gas). We paid extra for linen and towels - you generally have to take your own. You take your own beach towels.
You basically need to provide your own kitchen disposables - paper towels, bin bags, Fairy liquid - but it's easy enough to get these in the local hypermarket.
The main thing is surviving without a PC and TV. We took a portable DVD player and movies, and we picked up some other distractions in the local hypermarket - playing cards, jigsaws, colouring books (that's because I am not organised enough at home).
We used IKEA bags for beachy stuff and for laundry. If you plan to do laundry there, you really need something to carry it in. And on the laundry topic, it is probably easier to pack a few tablets from home than buy a whole box there.
We didn't do this, but a lot of people brought their kids bikes and scooters.