For Robin Wood and Tara...
http://www.aeclectic.net/tarot/cards/robin-wood/
Link above to look at some colors of the deck you are talking about...
If it's a White Tara and you want to play on the beautiful clear energy, I would try a clear quartz.
If it is a green tara--say a jade green--maybe a turquoise or jade or deep sea blue or green?
Robin Wood has a lovely rose-red heart shape in one of the cards, also the gold pentacle, etc...I do not have the Robin Wood, but I do have colorful decks where I alternate the stones...usually I have a heart-shaped stone in a color such as dark blue (Lapis) or recently, I bought a calcite heart that has jade green and golden-white inclusions.
Many people find their most pleasing colors--it can be a rose quartz, amethyst, jade, etc...and take that into consideration with a crystal.
Sometimes I put an unlighted incense stick for good smell vibrations...or dried lavendar or sage bits. It can get a bit messy, so perhaps you want that in a small muslin or gauze bag folded up near the deck...
Nothing is really needed, but adding little bits...it does make me feel a little more vibrant, intrigued and involved with using the deck...
Hope the ideas help.
Cerulean
