Once the tree goes up and dc go to bed, DH and i turn off all the lights except the tree lights and make whoopee under the tree 
The year ds was born i sewed a set of 25 small festive stockings that are tied to a string and draped around the balcony, that is the only advent calendar we have. They have a small chocolate in every day, we put one small toy in (lego blindbag or something) on the day of ds' birthday. One year he had this, plus Lego advent calendar (gifted) and my dad gave us a chocolate advent calendar - three was just beyond excessive.
Christmas day is:
DS opens his stocking on our bed.
Breakfast is pancakes, ds last year got a gingerbreadman-shaped frying pan in his stockkng.
Walk the dog.
Back to open the tree presents.
Relaxed lunch of soup, cheese and biscuits.
4/5pm-ish we go to a small beach town down the road which has a sand sculpture every year. The dog runs on the beach, ds can play with any new toys like remote control car or scooter etc. Atmosphere is great, we might have a hot chocolate or something.
When we get back, ds plays with his new toys and DH and i cook Christmas dinner for 7/8pm.
We are abroad, so it is difficult to get a lot of traditional British food, which doesn't bother me too much. I can make stuffing and mince pies myself, a roast is a roast. Pudding is something different every year.
We aren't religious at all but we have a knitivity, i have lovely photos of ds playing with it at different ages as it is so tactile and fairly unbreakable. For the first 3 years or so i gave ds the unbreakable decorations to play with on the tree and put breakable things either at the top of the tree or left them in the box. He has always been fascinated with the tree, of course, but quite respectful. I have a lovely photo of the tree decorated with police cars and Fisher Price people 
Christmas here lasts until 6th January, so plenty of time between 25th Dec and when school starts back to keep feeling festive, it doesn't feel depressing on the morning of 27th!
I honestly don't bother with Elf on the shelf, Santa footprints, reindeer food in the garden, Norad (tried it one year, ds couldn't have been less interested, it bored me and i'm a Christmas nut!), Christmas Eve boxes and other stuff. Definitely no festive pyjamas, duvet sets, towels... Don't have the money or the storage for all that. DS doesn't miss out as it isn't done here.
I have Christmas crockery for DS, tablecloths, some festive bowls for Film Sweets (capitals v important), Christmas tea, Christmas CDs, Christmas stories. And two giant round Christmas pudding cushions for the sofa 
Like pp, we have decorations from different places with different memories and we love reminiscing as we decorate the tree.
I have made a ton of stuff over the years for Christmas, many of our decorations, lots for DS' room, wreaths etc.