A "perfect souvenir" refers to an item or keepsake that is ideal for remembering a specific place, experience, or person. It is something unique and meaningful that represents a special memory or event in a person's life. Full definition
There you are always able to find shells, sand dollars, and other perfect souvenirs to take home and treasure. (grandcaymantimeshare.com)
It would be the perfect souvenir for any child making his or her First Communion, and also something special to buy for any Catholic child in Britain to commemorate the 2010 papal visit. (faith.org.uk)