There is a lot of festive cheer around Christmas. Hypermarkets like Makro would feature various offers on food stuff and Christmas items that are suitable for gifts. I saw their brochure and wish to share it here as you would be able to see a combination of local and imported items sold by Makro.
(Click on the picture on the brochure to enlarge)
They have mainly 2 main brochures- one with the Christmas theme offer which is included in this post. While the other brochure consists of their usual product offerings like groceries and everyday items.
For Christmas, they would stock up on additional items like Christmas theme and imported items. However if you are looking into more imported items, then Tops Supermarket would carry more imported choices. Generally Makro is visited by households and small business owners where items are bought in bulk.
A lot of the items such as Pringles, Ferrero and Cadbury chocolates are available all year round. There are also many other local brand of chips, coffee, snacks and drinks that are available.
Each year, there are many tourists who are spending their Christmas in Thailand. You can find popular brands of imported food sold throughout stores in Thailand. Alternatively I would urge you to try out local equivalent brands of items that are made in Thailand and available for a lower price with delicious taste.
In Thailand, the public holiday is New Year’s Day(1st January). Christmas is not a public holiday hence you would find a lot of offices and business open as usual on Christmas day. While the shopping complexes like Central are beautifully and lavishly decorated during Christmas hence the even though it is not a public holiday, the festive mood is very much felt. 
Since I stay in Thailand, I no longer have access to the instant White coffee from my home country. I have find and switched to local instant coffee (Khao Shong brand), the purple Capuccino flavor for a few years now. I find it is the closest taste to the more bitter instant White coffee that I was previously taking:
There is all year round including Japanese imported items which is available the whole year round:
Merry Christmas and Happy New Year!