Agree with others.
Do a food shop to bring with you (and raid the cupboards too!).
Swimming is great to lose hours daily.
Nature walks (and the nature centre is usually free for lots of stuff, talking to the rangers etc).
Walking and cycling around the site.
Using the various playgrounds, going to the lake and feeding whatever ducks or fish are there.
Bring waterproofs - one of DDs favourite memories of our first trip was that it rained a lot that week, and we did a lot of walking and cycling in the rain, and she got to see lots of molehills that appeared where there had been flat ground!!
And bring some board games, cards, and some colouring things - to do drawings, paper games, rubbings of trees etc. There is a big blackboard on the wall as well, so there is some chalk but a spare box can allow loads of extra fun!