One of the kindest spiritual gifts I ever received was A Gregorian Mass enrollment.  ( I hope I am remembering the correct term).  Thirty Masses celebrated on thirty successive days for the repose of the soul of my wife.  Perhaps you could do something like that.  

Even though you are not a "social person" please try to let your friend know how much you appreciate her or him, and you much you truly value the friendship and all that has been done for you. Sometimes a sincere message is appreciated more than anything else. But the value of any Masses that you have offered is unestimable, and would likely be greatly valued by your friend if you decided to tell him/her about them.

This is a personal question, and the individual in question is a member here, so I don't wish to discuss this using my posting name.

I have an extremely dear friend I met here, who has been, far more than this person could ever know, I think, such a blessing and help to me.  As many of us know, often our families are against our practising the Faith and true friends are so few and far between.

We are long-distance friends.  Any ideas on how I can show my gratitude and affection to this person, and how I can help spiritually.  I'm not generally a social person and I care tremendously for my friend but don't know what would be appropriate.  I'm  also consecrated to the Blessed Virgin according to the manner of St Louis de Montfort, so I'm wondering what in particular I can do as my works aren't disposable according to my intentions.  

Does anyone have special devotions they perform on behalf of their friends, etc.?

Answer:

The only way to truly be a friend to him / her is to deepen their faith with knowledge if you have something relevant to say OR ABOVE ALL encouraging MORTIFICATION.
It is not about "friendship" it is about saving their soul. We are permitted legitimate pleasures in life like good food and wine ( if not we would be Jansenits) BUT these are inferior to our DUTY to encourage others in the spirit of self sacrifice for the purpose of getting forgiveness for sins. They are a sinner and are in need of God's mercy. Encourage them to give up something they are attached to as a vice, or to undertake pain for the purpose of penance. This will help them more than friendly talk because when they do these things it is GOD who helps. It is no use being good friends if it comes to nothing, your friendship is founded on the commonhood of faith, it is no use after all to be able to say "see you in hell".

The way to heaven is paved with suffering. SELFLESS SUFFERING IN THE HOPE FOR FORGIVENESS.

On this subject, I was wondering if, in Heaven, do friends maintain that bond of friendship in a special manner? Do family members? (I know that spouses are no longer married, obviously.) Are there any Church teachings on this matter? I'd like to think so, but I don't know.

In the presence of the Beatific Vision, all consumed by perfect Love, there can be no sense of loss or sadness.  Would one be aware of others?  

regarding a gift for your friend, how very very kind!  If your friend is long distance and through the forum, you may not have their personal info to send a gift, but what about composing and emailing a spiritual bouquet?  

The saints are all friends with each other.