Decorations: real holly/ ivy wreath, decorated with pine cones, oven-dried fruit etc., a few candles, fabric-based and wood-based reusable decor (scour German Christmas markets for that kind of thing - they're awesome), maybe a few candles in glass containers.
Homemade cards (if you do them) with non-metallic toppers/ drawings/ die-cut paper decorations - all of which can be recycled. Or even, if you're feeling crafty, paper from pulp (shredded and soaked paper) with seeds embedded, which can be torn up and placed in the ground.
Presents: experiences, consummables (food/ toiletry set the person would need anyway - full size, no miniatures - a perfume they normally buy, second-hand items.
Food: locally-sourced goose/ duck stuffed with chestnuts and apples, seasonal vegetables, apple sauce (most festive vegetarian foods are nut-based, which are extremely resource-intensive, too, so not always a better choice). Homemade plum pudding.
The rest of the time? Good, old-fashioned games and board games, winter walks.
Low-key, very eco-friendly.