Hi Joanne23
Sunscreen and a hat is an absolute must. Even when the sun is not out, the rays can still be pretty harmful. I use the waterbabies sunscreen lotion and the milk spray. The spray is easy to use while they running in and out of water.
Snacks are essential, they can get pretty busy and that makes them quite hungry.
Toys for digging and pouring are great.
Always have one or two empty packets stuck in a bag somewhere. You never know when you need it for the dirty diapers, rubbish, or wet clothes. Extra clothes are essential (including a jacket).
Hope i've been of some help