In general, try to avoid anything made using plastics and other single-use materials. Instead, gifts made using materials such as organic cotton, hemp, wool or wood, for example. As well as this, rather than buying an excess of gifts, it is often better to buy less larger gifts with a greater emphasis on these sustainable materials.
It can also be a good idea to gift an experience (concert tickets or a cooking class, for example) in order to prevent waste and also add a more personal touch. You can even make something yourself, if crafts are something you excel at. Scented candles, bath bombs and homemade food hampers are all relatively easy to make. Here are some more ideas: https://littlegreendot.com/christmas-green-gift-guide-20-diy-gift-ideas/