As a mother of three girls, I can certainly say - Been there, done that! I do have to say that we were really lucky, 90% of the time, my girls were really good in restaurants (including restaurants here at home). On those rare occasions, I'd have to be really creative to keep them quiet.
First, when they were toddlers, I always fed them a little something before we got to the restaurant. That kept them from being starving while we waited. Then, a book or toy that they don't normally play with, maybe a new toy. Then, and this always worked for me -- Take a packet of sugar and let them lick their finger and dip it in the sugar. They loved it. By that time, dinner was served and we were fine.
When they got to be a little older, maybe 3 or 4, we would always bring their new friend (on each trip, they always got one new stuffed animal) to the restaurant. It was their job to be sure their "friend" was a good girl in the restaurant and minded their manners.
On occasion, if it had been a long day, I would just let them sleep through dinner. When they woke up later, I would get them some dinner.
Don't worry...it'll all work out!!!