Widebody Holiday Jets
OK, you've twisted my arm.
Aer Lingus used to send their 747s to the Mediterranean and Canaries when not doing transatlantic schedules. Likewise their 707s.
Aviaco would pinch 747s and A300s from Mother Iberia for their busy routes.
Britannia kickstarted the 767's bucket and spade career. Braathens wasn't far behind but in the end, they preferred their trusty 737s.
British Airtours used the early TriStars transferred from the parent, plus a few 747s from time to time. Caledonian continued their operation.
Of course, there are others but someone else can pick up the baton for now.