I'm thinking of denying my friend free fries after he did a similarly spiteful gesture weeks earlier
Why not just give him the fries like you normally do?
I'm tired of forgiving him for his petty 'friend' tricks.
Even though your friend might have done pretty tricks to you, you still shouldn't deny him food when he needs it. It's cruel and you can ruin your friendship further. There's no need to retaliate on him, it's better to forgive and forget.
I need to assert power.
It is not always about being the alpha and coming out on top. Sometimes it really is better to just forgive and move on, it will save you a lo of pain in the future.