We eat out a lot with our kids. One thing we try to do is review the menu ahead of time so that when the waitress comes for our drink order, we already know what we want to eat so it can be put in immediately. Saves us a big chunk of time. If DH and I aren't sure, we ask that she at least put the kids food in first and get it out ASAP so they're not waiting too long.
Things I've brought in my bag were books, crayons, coloring book pages, stickers. The kids get a kick out of looking at old pics on our phones. Sometimes we use our camera phones to take silly pics of ourselves while we wait.