I love the idea of casual Fridays. One day where you don't need to worry about what to wear. Just some jeans and a shirt. Pick one day a week - work week that is - and have it be your designated "casual day".
I like my causal day to be Friday, because by the end of the week I just feel blah. But yours can be any day you want.
By the way, I have those jeans in the first picture. Levi's 524. Amazing. That is all