To give your gift a personal edge include a letter telling them how you feel, a list of things you love or miss about them or for the less romantic a simple letter wishing them a happy christmas. It will make the gift seem that bit more special and will make them feel your presence with them at Christmas.
For the more technical out there a really special touch would be to include a video of yourself with a personal message, they will love being able to hear your voice but be careful not to make it too soppy as that could emphasise how much they miss you.