Rofl, don't pull the whole "I am not talking without a Lawyer" or it is going to give you a worse outcome.
You are under 18, no previous offences, and all you did was take a couple things.
It is petty theft.
Honestly, just admit what you did. Tell them the door was unlocked, so you went into the car and took what you saw.
Honestly, you told me you live in Ontario and you are more than likely just going to get a slap on the wrist.
Like I said, I was busted with $1500+ of stuff on me, plus a quarter of weed and a bong... never got charged.
I couldn't be fucked to read RuneScape's wall of text, but from what I have read he has KIND of hit the nail on the head.
Just remember, stay confident, if you lie, STICK to the lies because they are going to try and twist your words on you.
And one last thing, if the cop tries to strong arm you with the "If you don't tell us the truth then we are going to toss you in a cell", don't buy it, lol. That is one of the oldest and most retarded scare tactics they can pull and only the naive are going to fall for it.