Greatspear, obviously, though I dunno which one. Maybe Siluria's Tree, since it refers to the Great Tree and Yggdrasil is about as great as they come.
Armor is a toughy because there's multiple good candidates. I'm tempted to go with Kaiden set barring helmet, since it gives a good impression of "a Northman would wear this, absolutely". More options would include Blaidd's chestpiece or pieces of the Crucible sets. Helmet wise... very hard to say. Maybe the Elden Lord, maybe the Shaman helmet? Nothing I can immediately think of invokes the imagery of Odin's winged helmet.
Spells are a more difficult question. Lucidity comes to mind, since Odin is about as lucid as they come due to the whole all-knowing thing. It makes a lot more sense for Odin to be a sorcerer as opposed to a cleric based on his intellect, in fact, so we could just give him a litany of sorceries that'd be useful. Scholar's Armament would be fun if we gave him a greatspear that could benefit from it (Tree Spear?). Zamor's Ice Storm, Glintstone Icecrag, Freezing Mist, and Adula's Moonblade are all fun ideas due to the frozen north aesthetic but not really fitting of Odin's spear iconography (specifically for Adula's Moonblade).