One office i used to work in had a collection every payday where those that were members contributed a set amount (I think it was about £3.00) and there was a set amount if a member was leaving, a different amount for getting married and another amount if the had a baby.
If they chose to opt out of the scheme then fcuk them, but anyone that was in the club got the same, last week i put £2.00 in to get one of my colleagues a bunch of flowers as she was in hospital, a couple of years ago, i got the jaw broke playing cricket and a couple of my colleagues called round with a bunch of nah, 4 bottles of magners and a bottle of Smirf, also about that time one of the girls I was working with got married and almost all of us put £50 each to her collection (small tight knit group, and we were all invited to the wedding, reception and evening do).
What you contribute to a leaving do or a retirement do will be influenced on the size of the group you are working with and how well you know (like) the recipient.
I can think of one person I work with now that I would donate £100 if they never came back into the workplace.