Hello,
I respect and worship the Nordic pantheon, but am, by no means, an “expert” if such a thing actually exists. 
From my understanding of Odinn, sarcastically named 'The Mad" one, his is a personal sacrifice I believe. His ravens, Huginn (The Thought) and Muninn (The Memory) comprise the most essential elements of individual consciousness, as he is known to be a true seeker of higher wisdom and knowledge. So, just like attaining ‘true wisdom’ (as all the alchemists and Gnostics seek to do) requires valid thought and memory, Odinn needs and respects his ravens. It’s this wisdom search that supposedly led him to sacrifice his eye and hang from a tree to obtain Frigg’s Rune wisdom.
For me, I would consider gifts for his ravens, sharing with him information you’ve learned about life’s mysteries, ‘battling’ (not necessarily physically) the good, moral fight, and, even communicating with him daily - either through thought or other means - about all the above.
I believe, and I may be wrong here, that for most ‘deities’ the important thing is the personal relationship rather than gifts, etc. In other words, as you would with any potential physical friend, sharing yourself while learning about them is, maybe, more important than any physical offerings. Then, perhaps, once you’ve gotten to ‘know’ them to the level that’s possible, the offerings come easily. Not to mention how emotionally cathartic the process can be!
One warning: It is rumored that those that worship Odinn may come to tragic and early ends. I believe that this has nothing to do with Odinn. Rather, if there’s any credence to that rumor (which is very unlikely as it is a rumor), it’s because the stories of Valhalla, Odinn and Viking lore attracts and stimulates those more likely to engage in unsafe and potentially dangerous activities to ‘impress’ Odinn.
Here’s the thing - If Odinn is a god who intentionally sought wisdom (which he is as evidenced by the rhetorical sacrifice of his physical eye for a cosmic one), it would follow that, although he values bravery, reckless endangerment of self and others would absolutely NOT impress him. Quite the opposite, in fact.
One note on Loki - as you know, he is the ‘trickster,’ the one who cannot be trusted. Maybe, consider why you want to add him, then use the same ‘personal worship’ method mentioned above to figure out what makes him (and those like him) tick. Consider starting with a known token he coveted, like a necklace, as he is the openly passive-aggressive, anti-social discord sower.
My relationship with these elements or deities, even as aspects of my own character, is an active work in progress. I don’t know if any of this resonates with you, but I hope it helps, even if only in helping you decide what ‘not to do’! 