Recognizing that with the separation of church and state you can't favor one religious group over others, the most significant holiday for getting families reunited is Thanksgiving (not Christmas like in most European countries.)
Thanksgiving is always scheduled Thursday before the last weekend in November and it is one of the few days where Safeway, one of the main food chains, is not open 24 hours of the day.
Unless you are employed in retail, chance is that you have Friday after Thanksgiving off from work. Unfortunately, if you are employed in retail there is ever greater pressure for you to be working on Thursday as well because the big chain stores want to be open for the rush of shoppers who start holiday shopping on Black Friday. This day is the most popular shopping day of the year - it is named so because the bottom line of many retailers change from minus to plus, or goes from "red" numbers to black.
With four consecutive days off it seems like most of the United States is traveling. Everybody goes home to visit the parents and there is no end to how many people you can find room for. Inflatable beds, camping pads, and yoga mats cover the floors during this national sleep over party.
The story taught in school of the origin of this holiday goes back to the first pilgrims. As they had not had any chance to plant and harvest the year they arrived, they were left to the mercy of the indigenous population. The following year they returned the hospitality by inviting their neighbors to a great harvest feast. Hence, the fare is focused on local produce: corn, potatoes, sweet potatoes, pumpkin - and naturally the turkey. After the Civil War there were many initiatives for reuniting the nation; one of them was instituting a designated holiday for this first harvest commemoration.
The children learn the story of the pilgrims in school, they stage plays dressed up in bonnets, aprons and homemade cardboard-hats and it is one of the few occasions where Caucasian children can dress up in buckskin and feathers without being considered totally politically incorrect or non-PC.
When we first arrived in California we were beneficiaries of the hospitality that is so central to Thanksgiving. We were invited to join our friends at the home of a family we didn't know at all. Hey, a turkey is easily 10 kgs so a guest more or less is not that big a deal if he brings an appetizer and a bottle of wine. A great way to get to know new people.
The following year we hosted, and although it sounds like a big deal having 25 people for sit down dinner it really isn't as everybody are prepared to pitch in with a side dish, an appetizer, or a dessert. All the hosts have to do is to roast a ginormous bird and uncork bottles. (Naturally, if the family is flying in they can't bring a green bean casserole in their hand luggage and the host is busy in the kitchen for a couple of days).
The signature of Thanksgiving is Plenty with at least five kinds of vegetables. So unless you are a lot of people you may well have leftovers for the next couple of weeks. The smallest bird is normally around 7 kgs - before stuffing. It is quite a lot of food if you are only the two of you and aunt Thelma. Rumors are telling of an increased run on the emergency rooms in the week after Thanksgiving when people have eaten leftovers that should have been tossed out sooner or have eaten stuffing that wasn't properly cooked. A good move to avoid this is to ask more people to join you.
After all, Thanksgiving is about hospitality.