Received my free merchandise and drink notifications through the Starbucks App, the former being code 1018-FREE MERCHANDISE.
Simply present the rewards to the barista using the App. The most expensive tumbler is £14.95, so a nice additional reward for our custom throughout the year :)
My rewards are valid until the 11th Jan.
Update: No luck with the cafetière, but managed to get Frappuccino tumbler instead :)