The most literal answer to this would be 1 token = 1 animal egg since you are finding 1 animal egg from the banner in place of the single token you would normally find. In trading for animal eggs, demand will affect these values - it is ultimately up to a trading user how much they are willing to pay/how much they want to receive in exchange for an animal egg/token. To see the going market rate for the current animal eggs, I would recommend checking out the event trading thread here. It is worth noting that earlier into an animal egg's release, the more it is in demand and the more overpay is expected for it - if you are willing and able, it may not hurt to be patient in trading to find someone who is willing to trade it for a steadier amount closer to what the animal egg will eventually be worth ^^
|x|x|x┌─────────────┐ |x|x|x|x|they / he | trades |x|x|x||||||||||||||cs help |x|x|x└─────────────┘ |x|x|||"the hunt is everything, |xand the pack is always ready"