These are those cheap rings you get out of a gumball dispenser, or in a goody bag from a kid's birthday party. I don't know where my son got them, but he scooped up three and gave them to me as a present (wasn't a holiday or my birthday). He knew I liked sparkly jewelry. He thought he was giving me something precious.
And he was. It was a gift of love from his heart, as valuable as the dandelion bouquets he used to collect for me so many times during the summer and spring. All he saw was the beauty. When I look at them, I see his youthful innocence, hear his giggles, feel his tight hugs, and even smell the fresh scent of baby powder.
Memories like that are fodder not only for a story, but for a character. I have a novel, The Recalling, that is based on the memories a girl has for someone she lost. Suddenly finding a necklace stirs up those memories--good and bad. The story develops around those memories and the necklace.
Not just things, but our senses can revitalize memories. The smell of salt water makes my heart ache for the eastern end of Long Island where I grew up from seventh grade until my twenties. It brings back memories of going to beach parties, getting severely stung by a jelly fish (in the face), having my cousin spend summers with me, doing work around the old farmhouse my parents were restoring, and getting my first car. It also brings the sadness of the loss of five friends in car accidents, one the boyfriend about whom The Recalling is based on, my parents' divorce, and everyone in the family going separate ways.
The taste of homemade bread and apple pie returns me to our farmhouse kitchen when my mother baked. We had a fireplace in the kitchen, where the cat and dog would sleep in front toasty by the fire during blustery winter days, and where my mom would put bread on the mantle in a bowl to rise.
Songs and music evoke remembrances; the theme from Jaws gave me the chills (I lived on Long Island where the movie was supposedly set and sometimes there were shark sightings). Certain church songs bring me to tears because the music and verse are deep in meaning. And I will always rock out to classic songs like Bruce Springsteen's Born in the USA because I have to sing and dance with it, like it's in my DNA.
Use your memory or make up one for your characters. In my middle grade novel, even Jack the gray squirrel has memories of his brother being eaten by Fox, and his mother searching for food, but never coming home. These memories make him cautious and wary for danger. We are, in some ways, defined by our past; we want to hide it, or forget it, or relive it, or use it. Memories are snatches of our past. If characters are to be believable, they have to be more than a person doing something in the present. Characters have to have regrets and longings, fears and desires, motivations and inhibitions. Memories are Nature's way of keeping our past ever present and fluid, able to be summoned.
No matter the age, culture, situation, everyone (and it's believed that animals do too) has memories. It should be true for characters as well.