L.S.
What works for me is to have tons of snacks. I keep Gold Fish, the baby dried fruit and cherrios in my bag at all times. And I just give them to him a little at a time. If I give him a small plastic cup to go with them it is even better. He puts the snacks in and out, in and out.
A Friend of mine takes a protable DVD player with her and her daughter and that works for her.
Sometimes nothing works, but usually that works for me. Their attention span is very short, so you have to keep them pre-occupied at all times.
Also... screw everyone else. Who cares what anyone else thinks. Kids are going to be kids. Anyone who has kids will understand.
Good luck.