When the Winchester's home burned down, they lost everything that made a house into a home. Of course, the loss of Mary eclipsed that of books and plates, but as time wore on, the Winchester men found themselves mourning the destruction of other precious items – only a handful of photographs were salvaged from the wreckage, and so Sam would never see pictures of the four of them together, happy and safe. John had never removed his own wedding ring, but Mary's had disappeared in the inferno, and the loving inscription would never again be read. Dean's small collection of music tapes, labels written in the neat handwriting of his namesake Deanna, had melted away, and with it the only tie to his mother's family.
But some things had been salvaged, and one in particular would remain with the Winchesters for many years to come. Bought on a whim by John one day when Mary was newly pregnant with Dean, 'Bun' the bunny was small, soft and undeniably comforting. Over the years, it had survived dirt, vomit and spit, and emerged from the washing machine to soothe Dean to sleep.
For weeks after the fire, a lingering smell of ash and burning had caused John to attempt to throw Bun away, but Dean had remained stubbornly attatched, and eventually the smell dissipated. John never revealed afterwards how glad he was the bunny had remained, but the small toy had more than made up for the memories its odor had brought up.
On the road, Bun took the place of the comforting feeling of home. For a family reeling from an devastating loss, the small rabbit somehow helped them to regain their footing; Dean refused to sleep without it until he turned 10 and the bunny was passed onto Sam, and in times of stress a small fleece ear could be seen poking out from under the covers next to a blond head. When John woke hungover on the anniversary of Mary's death, he would find that one of his sons had tucked Bun between his neck and the pillow, and for a moment he would close his eyes and pretend he was still in Lawrence.
When Sam left for Stanford, he refused to allow himself to take Bun. Sitting on a thin mattress in an unfamiliar place, he regretted that choice, only to find that his brother had hidden the now threadbare bunny in his duffel.
As soon as Sam was allowed entrance to his and Jessica's blackened apartment, he had searched for Bun, and breathed a sigh of disbelief and relief at the toy's stubborn grip on existance. Dean hadn't even pretended to be embarrassed by the sight of his younger brother clutching the rabbit, simply running a finger across one grubby ear with a soft smile.
Bun was placed in a compartment in the boot, as safe as the brother's could make it as they travelled and worked, and after a hunt each of the brothers would take a moment to sit with the bunny hidden away in a pocket and just breathe.
When Dean rebuilt the Impala after the crash, he kept all of the touches that had made his baby uniqe. A toy soldier in an ashtray, Lego in the heating vents, Bun safely the boot last of all, and grinned foolishly as the car settled instantly into that comforting feeling of home.