My son and I were packing the car earlier this month to head back to college when my father emerged from the garage with a gift: a gallon-sized milk jug filled with sand.

In what’s become an annual tradition, my father fills a recycled plastic container – usually a Tropicana or Clorox bottle – with sand to put in the trunk.

The idea is that if the car gets stuck in the snow during the winter, my son can spread the sand under the wheels to help dislodge it.

My son is a senior. He now has four bottles of sand he has yet to use.

My father is a mechanical engineer who prepares for the unexpected. He has the perspective of someone who has driven the Lincoln Gap in a blinding snowstorm and been stuck on roads in sub-zero weather in Vermont.

I’m not sure he fully realizes that it doesn’t snow like it used to in the 1930s when he grew up in South Orange, New Jersey. Not even upstate.

Also, my son’s 2007 Subaru has four-wheel drive and the roads are plowed and salted.

When dad was growing up snow would get packed down and stick on the roads. The kids would go sledding on their Flexible Flyers by holding on to car bumpers.

My son didn’t want the sand. It takes room. It adds weight. He doubts he’ll need it.

I told him he had to.

“Your grandfather has put a lot of effort into this,” I said.

Also, I told him to be grateful there was only one. Last year, Dad offered to stock the car with more bottles for my son’s friends whose parents and grandparents seemed unaware of the need.

My son is a senior in college so it’s the end of an era.

He’ll graduate and won’t need to drive north every September.

Presumably there won’t be a good reason for Dad to fill another bottle of sand.

But I’m not sure that will deter him.

(Part of a series of life lessons based on conversations with my parents.)