Christmas Eve was a busy day on local freeways; hundreds of thousands of people came, as they usually do on all major holidays, from Southern California to Las Vegas. All of these people spent Christmas here in Vegas then headed back to Southern California the day after Christmas which is when the problems began. Note that bad winter weather was happening all over the US but for the desert southwest which is usually dry and sunny this time of year, many people were caught off guard.
First there were the back-ups. Highway I-15 which connects Las Vegas to southern California, becomes a virtual parking lot the day after any major holiday as everyone tries to head home at the same time. Usually this would just be a (very long) inconvenience as back-ups can range from five to sometimes 25 or 30 miles. The usual precautions for this sort of situation apply including leaving with a full tank of gas, taking food and water with you, and bringing entertainment for the kids to keep them occupied while sitting for hours in traffic (having a pee bottle isn't a bad idea either as rest stops/restrooms are sparse in the desert between the two major cities).
Unfortunately, yesterday's back up heading south became exponentially worse when the weather turned unusually cold and snowy which lead to a couple of long sections of the freeway being shut down overnight. In this case, a five hour drive on a normal day turned into a 36-hour nightmare for many holiday travelers. I am guessing that many of these drivers didn't have the basics for being stranded overnight in the cold and snow and very few were able to get to any of the small towns along the way and get a hotel room.
The moral of this story is that no matter where you are, where you are driving to, what the weather is "usually" like, or how fast the drive usually is, always be prepared to be stranded. To do this you need a full tank of gas, food for a few days, water for a few days, prescription medications for a few days, a pee bottle (or a DIY "wag bag"), a means of communication or two (cell and HAM radio), shelter and bedding (down blankets are a good, lightweight option which don't take up much space), maybe some chemical hand warmers, a first aid kit, entertainment options, someone who knows your itinerary and when to start looking for you, snow chains/cat litter/a shovel in case you get stuck in the snow, etc.
Check your car preps this weekend and ensure that if you were caught in such a situation, you would be able to take care of yourself and your family until help comes/the road clears.