Portions are huge, and taking leftovers home is normal

An American main course is often enough for two, and asking for a box to take the rest home is completely normal, not rude. Free refills on soft drinks and coffee are standard. Breakfast is a serious meal at diners: eggs any style, hash browns, and a plate of pancakes for a few dollars more. If you want real variety, look for the strip-mall restaurants run by immigrant families; that's where the best food in most American cities hides.