jmc

Since we move $\frac{1}{3}$ of the way along the segment, we will move $\frac{1}{3}(9-0)=3$ units in the $x$-direction and $\frac{1}{3}(6-0)=2$ units in the $y$-direction. This means that we will end up at the point $(0+3,0+2)=(3,2)$. Adding the sum of the coordinates of this point, we find that the answer is $3+2=\boxed{5}$.