Howdy Trekker.
Believe it or not, I don't think that has been ask that often, Yaris section doesn't get much traffic. Remember to try to search first next time if you think it's a topic too often asked.
Now about your question. I had a similar question...but it had to do with the base model with the power package and the S model. Here is the thread:
devil's advocate for yaris vs yaris s .
That said, though I forget what the convience package gives, between the S model and the base, the S has 15 inch wheels, 60/40 rear bench, the body kit, and the mp3 stereo. Interestingly, the S doesn't have power accessories. Not sure if the S or the convience package has ABS, but it's included in the power package.
Happy Shopping!
Dave