Return to one shared place
Walk the route once more, sit on the porch, or visit the park bench. A place can hold a goodbye when words do not.
Make one object permanent
A collar, tag, photo, or portrait can become the anchor. You do not need to preserve everything.
Write the ordinary things
Write what they did every day: the breakfast stare, the leash dance, the way they chose a spot on the floor. Those are the memories that fade first unless you save them.