Pick a few things and maximise those. Presumably the guy buying the 18 pack of beer chose something else.
You're factually correct that it is like premature optimizing code, but it is a hobby for quite a few people to optimize their lives. Others collect money. Some friends do board games. Or sport. (Personally, I spend a lot of time learning about some odd interests.)
I get my olive oil from an electrical hardware store around the corner from where I work - http://mroliveoil.com/page19.htm - how far do you go to get yours?
Lots of things are worth doing - often unavoidably so - but that doesn't mean you need to optimize each and every one of them until they're "right".
No, I don't "optimize" everything, but I do optimize a lot of stuff. If you like beer enough to consume 16 cans a week, then it sounds like something worth optimizing.
In general most things diet related are quite important to leave to chance. And if fun is involved too, then optimizing them can be fun too. You don't have to be OCD about it, just to try different brands and experiment.
>I get my olive oil from an electrical hardware store around the corner from where I work how far do you go to get yours?
Hmm, that's a bad example, as we value olive oil very much in my country, so I even have my own olive trees and produce my oil in cooperation with the village mill. Well, my parents do at the moment, as I live abroad now.