I will give you some advice.
On Monday, the temperature is17℃, but it is a little windy. On Tuesday, the temperature is 20℃ and it is sunny. On Wednesday and Thursday, it is a little cold. So I advise you to have your trip on Tuesday.
I think you can divide yourselves into four groups to do some interesting games. I think it will be very funny. Then you can fly kites in such a sunny day. At last, you can barbecue by the lake.
You can bring food and drinks that you like. I believe you will enjoy them very much.
Hope you can have a good time.
