Trying not to duplicate and of the above ideas...
Putting up the tree, anyone said that yet?
Decorating kids bedrooms... We go all out with the foil garlands hanging from the ceiling that you had in the 80s (only allowed in kids rooms, the rest of the house is tasteful 🤣)
Collect holly to put behind mirrors and pictures on the walks
Disposable bbq and toast marshmallows
Donate to charity of kids choice
Donate to food bank
Donate to toys on the table
Leave secret santa presents in local park
Make oven dried orange slices and decorate the tree with them
DIY snow globe (water, glycerin, and glitter on a jam jar with an old toy stuck on the lid)
Christmas disco bath (christmas music, glow sticks in the bath, disco lights /fairy lights in the doorway)
Make elf doughnuts (dip cheerios in icing and add sprinkles)
I also say that any family visits in December or christmas school activities (eg class party, disco, open craft morning) are an advent activity. It's like giving myself the day off
Indoor snowball fight (using white wool pompoms if you can remember how to make them)
Advent breakfast (christmas tree shaped crumpets with Nutella and sprinkles and marshmallows sprinkled with more sugar and just a hint of childhood obesity)
Make sausage rolls/mince pies/rum truffles/marzipan sweets