I’ll keep this short and simple: If you’re going out for a business lunch, decide what you’re going to eat before you get there.
Go online to get the menu if necessary. The last thing you want during a lunch when you need to be “on” is to spend 5 minutes poring over the menu while everyone else sits around waiting.
Plus, no one but you knows that you prepared in advance. When you only need a quick glance at the menu to decide your meal, you’ll come across as confident, self-assured, decisive.