The snow
The snow, which blankets the West Country, is a powerful symbol of isolation. Because of the snow, Eric, Bill, Rita, and Irene (and the rest of the inhabitants of the West Country) are forced to stay in and around their homes, as they're not able to venture out any further. The snow also reflects each characters' internal isolation, leading to the main conflict of the novel.
Pregnancy
At the start of the novel, Irene and Rita become pregnant. These pregnancies are slightly unexpected, but become important symbols of their new beginnings. After moving to the West Country, their lives change dramatically. They're neither as free, nor as happy as they once had been. Likewise, their spouses become consumed with other things -- whether it be work or other women.
Boxing Day
Traditionally, Boxing Day has been a celebratory holiday. In the context of the novel, Boxing Day is just as celebratory. It's a symbol of togetherness, as all of the inhabitants of West Country come together in an effort to build community. Ultimately, that doesn't happen, reflecting what often happens during holiday celebrations: drama.
Cottages
The cottages many of the families live in symbolize their rural setting, as well as their feelings of isolation. Vast plains of nothingness was dotted with cottages, showing the geographical isolation of the buildings, and the emotional isolation of those that live within them.
