Tonsure: The shaving of one's head so that the remaining hair looks like a halo came into style on the continent during an isolated phase, and so was not picked up until after the Council of Whitby.
Easter: The Celts all used a modified form of St. Jerome's method, called Celtic-84 after the number of years in each cycle. A slightly different way of calculating the holiday was proposed by Victorius of Aquitaine and later Dionysius Exiguus but was not immediately known by the British, Picts, and Irish. They were made aware of it in 602 and had all conformed by 716.
Penance: The prevailing continental custom was that confession was made publicly. On the British Isles it was done privately with a priest.
Peregrinatio: What had been meant as living a life separated from the material world while waiting for the secular became, among the Irish and British, an act of physically moving. It was common for churchmen to move from their homes, often leaving the island of their birth.