I just ate a big bag of potato chips and a Coke Zero, what will it do to me?

The potato chips contain a large amount of salt and calories, they could make you gain about 200 grams of fat (since it's a big bag). As for the coke zero. It doesn't have salt, sugar or calories but contains other unhealthy chemicals that make it taste like standard coca cola (and it's acidic)- so coke zero has a negative effect on your bloodstream. One bottle won't hurt you, but you should really drink plain water most of the time

You might gain half a pound. That's about it.

Time will tell. The chips are a lot of calories and salt, the soda is just nutritionally deficient and full of chemicals. However, it's not different than what a lot of people consume. How it affects each person differs based on their health, what else they consume, etc. 

It will eventually cause you to pee and poop

Pretty unhealthy snack. High carbs, high fat, high artificial colours, flavours and sweeteners. Nothing that is of team nutritional value.