In Toronto (were I am living) the average price of an average subway, pizza (slice), shawarma sandwich, etc. is around 5 to 7 dolars (including taxes).
If you want something a litle bit better you will have to pay more than that of course, and convencience stores are expensive.
If you live near of No frills everything is going to be cheaper and better to cook by yourself, but if you're not and you are lazzy (like me xD) prepare to spend some extra money.