The name "Holy-Rood" Day is synonymous with Holy Cross Day. The words Rood and Cross signified the same thing: the structure upon which Jesus the Christ was crucified.
A variant name for this holiday is Roodmas.
The Roman Emporer, Heraclius was claimed to have recovered a large piece of the actual cross upon which Jesus was crucified. Jerusalem had been plundered by the King of Persia, Chosroes around the year 615, and the cross had been part of the plunder. The day that Heraclius recovered the piece of the cross from the Persians was celebrated as Holy-Rood Day: 14 September.
Holy-Rood Day was celebrated as a purely religious holiday with the one exception being the collection of nuts.
Poor Robin's Almanack for 1709 contains the following verses:
The devil, as the common people say,
Doth go a nutting on Holy-rood day;
And sure such leachery in some doth lurk,
Going a nutting do the devil's work.
School children would go out and gather nuts and take them back to make of them presents to their school masters.