The icing on the cake

My dear colleague Míchel sent me this web page with moving stories of immigrants into the USA.

You may need to find out what these words mean:
- night shift - to make ends meet
- noodles - college- vending machine - icing on the cake
- raise /reiz/ 

Why does the speaker end with the expression "the icing on the cake"?
What does it mean according to you?

Listen to more experiences in StoryCorps.