I went to see John, one of my oldest (in many senses of the word, his personal duration, our joint working duration) colleagues in Europe this week. John and other mentor and I (see here) have worked together for over 30 years. Nearly 40, depending on how you count "working together".
To say thank you to both of them, I dug up old pictures. Snapshots. Non-digital. Pictures of animals we worked with, and animals that were pets. Pictures of us in surgery, and laboring with equipment, and the blackboard planning of experiments. We were all younger thinner and had more dark hair in those days. I scanned them in, and logged onto Shutterfly and made a book of what we've done.
The both loved it. One is Brit, one is South African, but trained in the UK, and stoic doesn't even begin to describe them. Very British Problems could have been written for them, by them., Needless to say, there were rough moments in the past, when I tended to lead with my emotions instead of my brain. But that was a long time ago, and perhaps they learned something from me, too. They loved the book, and said so to me.
As good as it is to hear thank you, from one's students, one's trainees, and one's children, the reflection back I've gotten from my efforts to say thank you are far more gratifying.