Depends on where you are having your lunch

- basic business and dinning etiquette is a must
- try to eat something before hand (no garlic, no onion, etc.), so you don't feel the urge to eat during lunch interview
- salad usually would be a good choice and avoid the things that might stick on your teeth (broccoli, black beans, etc.) and be messy to eat (burger)
- order modest amount/value (if fine dinning)
- eat quietly
- don't talk and chew at the same time