For the goliath, are you looking for something that will encourage him to cast more magic, or to suit his current play style? Perhaps a bearskin coat that gives him resistance to cold and bonus to intimidate/survival could be a good idea, especially if he hears about a rogue Polar Bear that is terrorizing the local region.The gift from the treant may be a magical wooden shield that can give resistance to slashing or fire damage (Axes/Fire=Bad). Or if you have anyone who uses spears, bows, or javelin (basically any wood) they can get some magic ammunition.
Another thing could be a draught/root from the treant that can be used to cast the Enlarge spell, either once a day or as a consumable. If the goliath likes to be the biggest bear around, then that will be up his alley too.
Random ideas:
-Root Boots: You plant your feet into the ground and your movement speed becomes 0. While rooted, you regain 1d4 HP at the end of each of your turns.
-Manure Bolts: Requires a successful Nature/Herbalism check. These bolts are made from the party's last... disposal. On a hit, they do 1d4 damage and the creature must make a DC 11 saving throw or be poisoned until the end of it's next turn.
-Steel Rose: Requires attunement. A flowery decorative +1 mace that gives the wielder advantage on Charisma checks when engaging with humanoid who may be attracted to them.
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