One great way to eat cheap is to order water instead of tea, a soft drink or alcohol. Just not ordering sodas can save you five bucks, if two are eating.
Sometimes, appetizers are as big as a meal, and may be big enough to split. One local place has these nachos as an appetizer, and they have *everything* on them. My husband and I will order the nachos, each eat half and be very satisfied.
Eating at lunch is almost always cheaper, too. Also, ordering combo plates like a soup and salad or sandwich can also save a lot of money. At Panera Bread, for instance, their "pick two" combos are about $7, where a full sized sandwich or salad will run $8-$10.