Quite a few hotels do a free breakfast. It isn't that great a quality but there is usually fruit, yogurt, oatmeal, and cereal, and hot food like scrambled eggs, waffles, and sausage. Some do free dinner on weekdays, usually there is only one option, it's worth looking to see what the week's menu is.
Quite a few restaurants do 'earlybird' and 'happy hour' specials where food and drink are reduced price in the late afternoon/early evening. They may also do reduced prices on different days e.g. kids eat free on Wednesday. When you are out and about it's worth looking for things like that. A lot of places offer smaller portions at a lower price at lunch.
Restaurant portions tend to be large, most places don't mind if you share a plate, you may need to pay a sharing charge (although I never have had to), they will also give you an extra plate to use for sharing a meal.
If you are eating at a fast food place I'd allow about $6 a person per meal, if you are eating at a medium range restaurant then around $18 per person per meal (including soft drink). Cocktails are around $10 each, beer about $3.50 - $5.00, Soft drinks around $2.