It's the little things, Steve finds, that make his and Peggy's relationship what it is. The grand gestures and the milestones are important too, but they don't build the substance of a relationship.
Whenever they're camped somewhere that wildflowers grow, Steve picks a bunch for Peggy. They aren't grand bouquets, just little clusters of whatever is around tied with string or grass or wire, but he uses his artist's eye to try to make pleasing combinations, and Peggy seems to like them. He never gives them to her directly, merely leaving them by her tent or bedroll, but he sees the smiles she gives him afterwards.
Peggy tells him about Michael on the anniversary of his death. He notices that something is bothering her, and gently asks if she's alright. Peggy normally prefers to keep her grief private, but something in Steve's eyes tells her that he'll understand. He does. He listens in silence, but with a gentle attentiveness that leads Peggy to say more than she ever thought she would. She tells stories about the games she and Michael used to play and the mischief they used to get into. It's good to remember those times, and not just their last fight and the day the telegram came. Steve doesn't say anything when she's done, merely reaching out to hug her for a long time.
Steve has always liked to draw the world around him. During the war, he draws all the Howling Commandoes multiple times, but he comes back to Peggy the most. He still draws her after he wakes up. Sometimes the pictures are of his memories, but lots of them feature her in his new life. He sketches her scolding Tony like she did Howard, sparring with Natasha, pranking Clint, standing in the back of Avengers strategy meetings. It's all impossible, but it sometimes makes her feel closer. The first time he draws Peggy after he finally makes it home to her, Steve is struck with awe that this isn't make believe. He can draw Peggy in his everyday life not just because he thinks of her, but because she's there.
Steve does most of the cooking after they get married. He likes it, he has more time for it, and, frankly, he's a better cook than Peggy is. His super solider memory comes in handy as he can recall the recipes his Ma used to make and the ones he learned in the future. Steve doesn't know a lot about British cooking, though, so he goes to Mr. Jarvis to ask how to make Peggy's favorite foods from home. Mr. Jarvis is happy to help him, and the delight on Peggy's face when Steve surprises her with a treat she loved as a child is priceless.
Steve learned how to do hair from the girls on his USO tours, and he does Peggy's hair for her nearly every morning. Sometimes it's leisurely and relaxing, and he gives her kisses in between the steps. Other days it's rushed, a practical help to Peggy as she eats breakfast and plans strategy before dashing out the door to save the world. Either way, it's a little moment for them at the beginning of every day, and they treasure it.
In the end, when Steve is old and gray and looking back at his life, it's the little things that count the most.