a haversack large enough to carry several small children (OP20)
A bag or backpack for carrying food on an outdoor trip.
Using this word to refer to human provisions is a little like speaking of "feeding and watering" people or referring to food for humans as a "nosebag", because like those expressions 'haversack' originally was used to refer to feeding horses rather than people. The word was originally borrowed from French (which spells it differently), which had borrowed it in turn from German Habersack, and meant a bag used by cavalry to carry oats for their horses. In English, haver is a dialect word for 'oats', used in Scotland and northernEngland. (NSOED).