We have loads around Christmas. We get the Christmas music CDs out on 1st December and play them every day from then on until the big day. We decorate the tree together on Dec 13th (my grandmother's birthday, RIP). We have a card-making day and a decoration-making day the weekend after they break up from school. We do the Xmas PJs thing and the kids get a 'Christmas kit' on Xmas eve - PJs, hot choc and marshmallows, a board game, a Xmas film on DVD etc.
We don't have Easter traditions, really, but we have just planted some summer bulbs for the first time and I'm thinking of making this something I do with the kids every year.
Otherwise, it's the simple things, really, isn't it? Lots of it is seasonal.
We go and see the bluebells when they come up. We go for an autumn walk on Hampstead Heath. We have a picnic in Hyde Park every summer, and we always try to swim in one of London's lidos every summer too (brrr).
I remember my gran taking us to the sweet shop every Friday after school or to Wimpy for lunch during every half term. We do similar things - jam doughnuts on Fridays after school and lunch in a cafe during half term.
Me and DH do 'mummy days' and 'daddy days' with each of the kids separately, too, so they get special time with us. Usually once a month if we can manage it.
this is a lovely procrastination activity for someone who should be getting on with writing a report