Good dark pants, long sleeve dress shirt, and solid color sports jacket that can look like a suit jacket.
Don't button the jacket and be sure to have a good looking belt. If it's a casual place you're at, you carry the jacket.
More casual you can fold (not role) your sleeves up two turns. If you hit a more dressy place, fold your sleeves down and button them. To be more dressy, put on the jacket, but do not put your shirt collar out over your lapels.
You should carry a tie in your jacket pocket in case you hit a place that requires one. A quick trip to the restroom to put it on makes you ready to go first class.
Carrying the jacket looks cool, even if you have no intention of wearing it that day. You can drape it over your arm, or if your in a Sinatra mood, carrying it over your shoulder.
If your jacket has an inside pocket with a button, it's a good place to put your glasses, where they won't fall out. Be sure to wear black leather shoes with this and you'll be looking Bond no matter the time, place, or ocassion.
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