Invade a park playground you haven't been to before

Visit friends
Cook biccies
Beach
Lake
Camp in back paddock
Camp in front paddock
Walk in the bush and have a picnic
Walk the dog/s
Go to botanic gardens

Low cost
Buy weird stuff from recycle and take it apart
Go to a workshop and get wood scraps. Buy some nails, build and paint
Construct with big boxes (beg from furniture/whitegood stores)
Go to a "pick your own" farm
Plant a vege garden