We have a pile of notecards and a shoebox prominently placed in the kitchen. Life is busy, we don't 'scrapbook' but we do take 10 seconds to write down an interaction, a joke, a poignant thought ("out of the mouths of babes") etc. and toss it in the box to be sorted through, recollected, and organized in the empty nest years.
There will come a point in these young ones' lives where they may need to be reminded of who they are--who they've always been. These little cards will come in handy.