Discerning Sodium bicarbonate
Without additives its a bit hard.

You can test easely if it must be it or not, if you put a bit of it on a flame you must see a yellow flame which means there is sodium $\ce{Na}$ in the compound. Like this.


And to be more sure if you pour some acid (like ethanoic acid or vinegar) it must makes gas. Now if you want to verify that this gas is carbon dioxyde you can try to do the reaction on a glass or whatever you want, light a candle and pour the gas (which is inside the glass) on the top of the flame, if the flame disappear it must be carbon dioxyde. Exactly like in this video obviously you don't use backing powder but your product.. 

You can also use a solution of limewhater but you musn't have this at your home...but if you have you must obtain this: (but you need to pour the gas only in your solution!) so its not really easy at home.


So if you do all this experiments you can say its $\ce{NaHCO3}$ but its impossible to be sure at 100% whitout doing an Infra-Red exams for example. It can be mass spectroscopy or RMN.. but obviously not at home, and you can detect all additives if they are.

Hope it will helps you a bit,
Friendly.



NB : If you are not sure don't use it for your food.. :)