Depends how well you know them, but once, for acquaintances celebrating a Ruby anniversary, we filled a box with all sorts of dark red candles, some scented, some not, a couple of ruby glass candle holders, a candle snuffer and a box of tapers wrapped in red velvet. We put the lot in a red-covered box lined with dark tissue paper and tied it with a red velvet bow. we've done variations on a theme for loads of other 'big' anniversaries and birthdays since then, and the boxes are always very well received.