Our stockings, growing up, always had:
Something to eat
Something to read
Something you'd like, and
Something you need
So things like new knickers or socks or hair bobbins were common. The "eats" were always: A red apple, a green apple, a satsuma, an orange, a banana and a kiwi, along with a 1/2 pound box of sweets (like wine gums - you know the ones you only every see at Christmas?).
A book
And maybe something else small to go with the big present.
I do a similar thing with DD's stocking - it's bigger than the "pair of everyday socks" we used to use, but not huge. (And you can always downsize the stockings if they get "lost").
Look out for things like pages of stickers, party packs of bubbles, pound shop toys, Lidl and Aldi are great for small things, stationary sales at this time of year for crayons/pencils/colouring books/notebooks....
As for other things, you can always get the kids to make things that can be given as presents to others. Potato stamping for wrapping paper, cards or even pictures to be given as Artworks. Making paper chains for decorations, or folded newspaper people/snowmen/angels/snowflakes. Or using paper plates to make snowmen/santas to hang from windows (like kitchen or bedrooms).
Cookies, sweets, mulled wine spices sets....kids can all have an involvement in those (counting out specific numbers of peppercorns, cardoman pods and cinnamon sticks can pass an hour or 2).
Painting old jam jars and twisting some wire around the rim as a nightlight holder.
Putting cloves into an orange.
There are LOADS of different ideas on the net if you go looking - One pretty thing is a great one for rounding up ideas and linking back to the original websites for instructions. www.oneprettything.com/
I try to do something every day in December with DD leading up to Christmas - very little is religious. (And I pop 1 chocolate snowman or santa - I get net bags of them in Aldi, into the advent calendar each day too).
We go for a walk and collect pine cones in the woods, and another afternoon we'll paint those to make decorations.
I print out lots of Christmas colouring and activity sheets (wordsearches, maths puzzles...) from the net.
Going to see Santa.
Writing the all important letter to Santa.
Going into town one afternoon to get HER shopping and have a hot chocolate together.
Trying to get to a carol service or some music somewhere (she loves music).
Make Christmas cards for Grandparents.
Read a Christmas story most nights, or watch a Christmassy movie one afternoon.
Listen to Christmas music and dance around the kitchen.
Decorate a part of the house together (a part that they can be as kitcsh as they like, I do the sitting room myself, although she also helps with the tree another day).
Somedays, I make the activity a crafty thing, but don't put it into the calendar - I put a clue and make a treasure trail around the house with it (only about 3 clues though, as it is usually weekdays that I think of that), with the craft materials at the end.
Go visiting relatives.
Hope there's a few ideas in there for you.