OK - you are ready for a Picnic. Here are a few things that you should consider taking with you:
First Aid Kit
Drinking Water - of course your food that you want to enjoy while there
Insect repellent
Hand Sanitizer
Damp wash cloth
Disposable eating utensils
Napkins or paper towels, wet wipes would be added bonus
Beach Towel ( can be used to cover table seat, used for ground cover or going for swim)
If you have, a folding chair
Sunscreen, hat or other head cover, long sleeve light weight shirt and sun glasses. All these for your protection from Sun