Nothing was visible from the site but sand and sea.

There were no trees there and nothing green;--neither was there any running water.

But there was a long, dry, flat strand; there was an old boat half turned over, under which it was proposed to dine; and in addition to this, benches, boards, and some amount of canvas for shelter were provided by the liberality of Mr Cheesacre.

Therefore it was called Mr Cheesacre's picnic.
But it was to be a marine picnic, and therefore the essential attributes of other picnics were not required.

The idea had come from some boating expeditions, in which mackerel had been caught, and during which food had been eaten, not altogether comfortably, in the boats.