Over spending on presents is easy to avoid, everyone really understands now that they have everything they need, so you are really just giving a token and it doesn´t really matter how much it cost as long as you think they´ll enjoy it.
You can find great gifts in charity shops, as long as you have time to make repeat visits multiple shops, I don´t think this method is perfect though as you will end up with at least one "it will do" present if you rely completely on charity shops.
Consumables-food, drinks, candles, soap etc are excellent to stop the build up of stuff, especially if you can get a more sustainable alternative eg. soya wax candle in an upcycled container or handmade soap loose, are another great option.
Homemade is another option-crafts (useful stuff using upcycled materials) or food.
Vouchers are the ultimate no build up of stuff gift, but I am not a huge fan because of the specific monetary value attached.
Athough I don´t choose the gifts to be cheaper (and not all of them were), approaching the idea of getting presents with sustainability in mind meant that I ended up spending less.
I am no longer a user of wrapping paper or gift bags. Everything this year will come in newspaper or salvaged brown paper. You can get paper tape or twine to fasten the packages, but I used ribbon taken from previous presents or elastic bands from bunches of fresh herbs. The tags were made from a cardboard box, or from a sticker sheet that someone had accidentally printed an invoice for me on the back of (I am pretty happy that they didn´t reprint it for me). Total cost zero.
I spent much less money here because the vegetarian option is usually the cheapest thing on the menu, or there is nothing vegan so you end up with two side orders instead, and there isn´t even any point in looking at the dessert menu!
When you make everything yourself, you put more time and effort in, but the ingredients do end up being much more affordable than pre-made dishes. Plus animal products are generally more expensive.
Dressing for the season:
If you are working towards a capsule wardrobe you aren´t going to fall into the trap of buying a Christmas jumper (or skirt) or a new outfit for your Christmas party. You are also used to wearing the same thing again without washing in between so you never end up with "nothing to wear" situations.
Much like my diminished need for a Christmas jumper, I am no longer interested in buying a load of stuff that is going to be in a box for 11 months of the year. And I am certainly not running out to pick up anything disposable. It doesn´t mean I don´t decorate! Last year I painted the windows (with my niece and nephews) which was pretty festive. I also hung strings of cards (which I added to this year with the new cards that came).
Have never been a big deal for me, I never got into the habit of sending them. But if you did and you wanted to be more eco, you could opt for email or photo message distribution which would also work out cheaper.
All in all I think if you are conscious of the environment you don´t get caught up in a load of the hype and consumerism of Christmas, so you end up spending less.