Here's what we have done on a Saturday earlier this summer:
Picnic lunch c/o food delivered to the house, hammock time, gardening game, police game, fireman game, digging with trucks, tag, swings, slides, Play-Doh, playing house, collecting maple keys, bug examination, trying on sunglasses, pulling grass, watching 7 year old neighbour with butterfly net, taking pictures, chasing birds away from the flowerbed, plane-spotting, leaping off rocks, transporting bricks, snacking on fruit, tricyling on the deck, singing, foot races...