Use the following trick to get some items and gifts before you leave the castle. When playing as a human noble, after you go to your brother Fergus' room but before you leave, to go to bed ask your dog "Do you see anything interesting?". If he brings nothing back, ask him again. By doing this you will obtain the following items:

Piece of wood, which is a tier 4 mage staff that has a +1 Constitution and +10% Nature Resistance.
Found cake.
Dirty pair of pantaloons.
Tangled ball of yarn
Bottle of Garbolg's backcountry reserve.
Greenstone or elfroot.
Unique but seemingly useless Codex entry.