I always find old holidays and special days and customs fascinating, and as the 29th of May is Oak Apple Day in England, here is an extract about Charles II and the Royal Oak, from Chambers' Book of Days, 1862:
"Among the acts passed by parliament immediately after the Restoration was one enacting 'That in all succeeding ages the 29th of May be celebrated in every parish church and chapel in England, and the dominions thereof, by rendering thanks to God for the king's restoration to actual possession and exercise of his legal authority over his subjects,' &c. The service of the Restoration, like that for the preservation from the Gunpowder Treason, and the death of Charles I, was kept up till the year 1859.
The restoration of the king, after a twelve years' interregnum from the death of his father, naturally brought into public view some of the remarkable events of his intermediate life. None took a more prominent place than what had happened in September 1651, immediately after his Scottish army had been overthrown by Cromwell at Worcester. It was heretofore obscurely, but now became clearly known, that the royal person had for a day been concealed in a bushy oak in a Shropshire forest, while the commonwealth's troopers were ranging about in search of the fugitives from the late battle. The incident was romantic and striking in itself, and, in proportion to the joy in the having the king once in his legal place, was the interest felt in the tree by which he had been to all appearance providentially preserved. The ROYAL OAK accordingly became one of the familiar domestic ideas of the English people. A spray of oak in the hat was a badge of a loyalist on the recurrence of the Restoration-day. A picture of an oak tree, with a crowned figure sitting amidst the branches, and a few dragoons scouring about the neighbouring ground, was assumed as a sign upon many a tavern in town and country. And 'Oak Apple-day' became a convertible term for the Restoration-day among the rustic population.... In many old-fashioned and out-of-the-way places, the 29th of May is still celebrated, in memory of King Charles's preservation in the oak of Boscobel, and his Restoration."