Hermione,
This is Essence of Moonstone, a very rare element I thought might come in handy for your schoolwork (and your "extra-curricular activities"!) I'm sure you already know it has over a hundred different uses, and that you will discover new ones soon...
Ron,
Merlin knows I'm not as good a knitter as Hermione is (a fine quality in a girlfriend, by the way) but hopefully this will not serve as anything else than a scarf ( yes, I know that vile orange sweater you got last year ended up as a sling shot for garden dwarfs - no, I won't tell Mum.)
Dear Harry,
I didn't quite know what to get you for Christmas that you don''t already have, but the colour of this malachite pendant matched the colour of your eyes, so... I read in a book that this stone protects the bearer from bad dreams - I don't quite know what to make of crystal magic, so you'll have to let me know. I hope you like it!