Secondhand. I get 90% of presents secondhand. Buy now if you can, people put prices up from November.
Christmas lists - write now, heavily supervised, emphasise that this is an “ideas list” for Santa to pick from, and no changes allowed!
Don’t exchange gifts beyond immediate family. If you do normally and are worried about this, try suggesting a secret Santa (with strict budget limit!).
Depends a bit on age of kids, but buy necessities as presents. New (secondhand!) kit for sports, school, etc, can go under the tree.
Don’t get sucked in to stuff being “special” because it’s Christmas. Normal chocolate or potatoes or cheese tastes just as good as the fancy stuff.
If you’re really struggling, there is nothing wrong with asking for help. There are all sorts of present giving drives going on at Christmas, community larders giving out food, etc. Take the help that is on offer.
If you can work out whether there are any specific things/areas you normally spend on, I’m sure people can help you with specific ideas.