Lipsticks, because I don't have that colour but I do think I suddenly need it. And I buy a lot of eyeliner too but that's because I use them up quite quickly.
I've been buying alot of their lipsticks.. though i do have a soft spot in my heart for their foundations and dont mind trying of of the many, spur of the moment!
I primarily go to MAC for lipsticks and eyeshadows, but the one thing I repeatedly purchase are the wipes. It's almost time for me to get new concealer. After years of using it, I've almost out.