One central similarity between these two characters is the way that both play the role of sidekicks or loyal friends and servants to the characters that they are paired with. Let us remember that Adam is the loyal servant of Oliver and Orlando's father, who when he challenges Oliver about his treatment of his brother, then leaves with Orlando and journeys into the Forest of Arden with him, giving Orlando his life savings. Adam is clearly persented as the model loyal servant that lives his life based on concepts such as virtue, honour and loyalty rather than trying to selfishly improve his own station in life. Note how he practically begs Orlando to let him accompany him:
Let me go with you.
I'll do the service of a younger man
In all your business and necessities.
There is definitely a common feeling of love and kindness between Adam and Orlando, and it is important to note the way in which after Jacques gives his famous "Seven Ages of Man" speech, which concludes with a terrible image of old age as isolation and oblivion, Orlando then enters straight away bearing Adam on his back, pointing out how wrong Jacques is.
Celia bears many similarities to the character of Adam, but in the way she acts as foil to Rosalind. Even though she is not a servant but a noblewoman, she, like Adam, decides to leave the court with Rosalind, in spite of the dangers involved. She plays second fiddle to Rosalind, her companion, and serves as the go-between in her relations with Orlando. As the play proceeds, her character receeds, yet her loyalty and friendship towards Rosalind remains constant.