The gifts in "The Carol" MV indicate Loona members in which HeeJin, HyunJin, and HaSeul is eagerly waiting for ViVi to join LOONA 1/3 unit. For example, leader HaSeul is carrying 11 gifts signifying the 11 members of Loona. #LOONATHEORY cont. below 
In the beginning of the MV, the first member HeeJin is carrying one gift. She walks to the place where the second member HyunJin is eagerly waiting for her. After meeting HyunJin, they both carry two gifts. (HyunJin doing her cat thing) 😆
HaSeul is waiting as well but also checks the clock to see if it's 4PM yet. Her waiting is in anticipation of the 4th member of Loona to join them in one unit. We also see scenes where members are counting all the way up to 3 but stops short of 4.
When Heejin and HyunJin finally arrive at HaSeul's location they shyly present 5 gifts. This is because the member who will be joining them in the unit is the 5th member ViVi instead of 4th member YeoJin.
They now each have 5 gifts and while heading to the party they also stop by a chocolate store to buy some chocolate for the Valentine girl.
The Valentine girl is of course ViVi who was revealed the day before Valentine's Day and on Valentine's day, (LOOΠΔ 1/3) 3월을 기다려 (Valentine Girl) Preview was released. (3월을 기다려 means Waiting for March)
In that song they sing about ViVi as the Valentine Girl and when they also say that "I can't wait for the next month so that I can meet you." The next month is when Loona 1/3 unit will debut with ViVi.
During the party the members can't wait to see who will be joining their unit. They had to choose the correct gift to open to see who was the member or they'll get surprise feathers.
The Carol MV was released on 2016.12.15 along with Let Me In. BBC had already planned for the 5th member to join Loona 1/3 unit long before YeoJin was introduced. To wrap up, I'll leave you with all the pink (ViVi's color) hints they were giving us. (pajama, phones)
Pink headphones
I forgot to include HeeJin carrying one gift in the beginning. 😅
