Surprise Birthday Party !!!

We are planning a surprise birthday party to my neighbour which is today.
I know that he is not expecting it but thats the fun of surprise parties
I love doing such things but my friends have thrown all the responsibility on me.
So I have to start everything as soon as I leave office.(scratching my head)
Order the cake and then buy some balloons and a gift as well ...
And I am planning to decorate my balcony since we cannot do it in his room without raising any suspicion.
I am so excited...
Any ideas for a gift?