From just after the 80s (as I started this when I hit 16), I have a personal tradition of having some time one quiet evening - with only the tree lights on (maybe there is a fire lighting or a couple of candles as well, but no harsh lights), lying on the floor under the tree with a nice drink (it started with a cheeky Jack Daniels when I was 16 - but isn't always alcohol) and thinking about the year that is coming to an end and planning ahead for the new year - just some quiet and peaceful contemplative time. And lying on the floor gives a different perspective.
As DCs in the 80s, there were always those gold lame chains on the ceiling. Since I had my own DD, I have a tradition of giving her a shoebox in early December filled with different coloured strips of paper and a DC-friendly scissors and roll of tape. So she can start and stop at her own pace when she needs distraction for a few minutes at a time to make paper chains - the 10 minutes while I was cooking dinner, when she was bored on Saturday afternoon for an hour, etc - and by the time we decorated close to Christmas, she tended to have long chains for the hall ceiling and sometimes her room as well.
Sharing an annual between the 6 of us DCs, being allowed a biscuit from the single tin that would arrive into the house, and the real treat of fresh fruit all of our own!! (Santa always brought each person about 5 or 6 pieces of fruit - a red apple, green apple (nice granny smiths), orange, satsuma, banana and something like a kiwi or peach or plum etc - 1 DC got a pineapple one year!! But as normally there was a box of golden delicious apples and no other fruit, this was HUGE for us all - some ate theirs on Christmas Day, others rationed theirs over the whole holidays and sometimes there was war if 1 greedy guts raided another person's carefully hoarded stash....).
Santa also brought each person a different 1lb box of sweets - which was also a huge treat in our house.
We normally had milk or water to drink (squash just disappeared far too fast between 6). But at Christmas, DF would go to cash and carry and come home with about 4/5 slabs of cans of fizzy drinks. When the slabs were only available in cash and carry's - not like now when they are in normal supermarkets. But there would be a choice of fizzy drinks over the holidays - and everyone would be allowed a can for dinner a few different nights, and we'd also get a can for the Christmas present opening (and DF had mixers for visiting adults). We tend to buy cans ourselves, as we drink so little fizzy stuff that it was going flat in bottles, but it can be nice for everyone to have their own choice.
Making orange pomanders with cloves to hang.
Helping DM to stir the pudding and everyone making a wish.
The difficulty in finding quiet hidey-holes to work on making presents for DSiblings and DParents, and wrapping them in secret without others seeing them. So lots of secrets and shushing and "can't come in here" shouts etc...getting especially frantic once school holidays came (and there were 6 different people trying to do it - or 4 trying to do it and 2 smallest people looking for playmates....).
The Christmas Party for DCs of DF's work - in the local social club, with a DJ and the old fashioned disco lights that were just coloured bulbs and real vinyl, everyone got a drink and bag of crisps, Santa (in a cotton wool beard and red dressing gown) came and everyone got to meet him behind a black bin bag curtain hiding the space around the snooker table, then more dancing - and then another 3 hours once it was all over while we'd help clean up torn paper/empty crisps packets etc and get another drink (a 2l bottle and load of "shorts" glasses to share with whatever other DCs were abandoned by their DPs still in the bar chatting - it was the same DCs we'd see twice a year, at Santa party and summer sports day), then run around in the dark on the soccer pitch!!
Actually sitting down at the kitchen table to write letters to Santa. On paper, with neatest writing, and not being greedy. All 6 together (so older having to help younger ones until they were good enough at writing). And then all letters going up the chimney together (no fire that night in mid-December, and again on Christmas Eve).