Having cake in Sweden is a very traditional was of celebrating, but it is a little different than I am used to. If I were truly Swedish, I would have bought my own cake.
Whenever someone has a birthday, achieves something, gets a promotion, graduates, etc., it is that person who buys or brings their own cake to celebrate. No need to worry about who will bring the cake, it is always the person of honor. The upside is you can always buy your favorite type of cake for your own special occasion, instead of pretending to enjoy the flavor someone else picked out (Although, don’t we all buy princess tarta anyway?).
This tradition is very strange for me (And other expats I’ve met), as I wouldn’t ever think about buying my own cake in the U.S., but wait for some one else to do it.
If you are congratulating someone is Swedish you would say “Grattis!,” but if you say “Gratis” instead you are saying Free.