I was on my own with DS when he was 5 weeks old when we got caught on a motorway closed because an fairground ride had fallen off it's lorry. It was the hottest day of the summer, and we were there for hours.
I was bf, so that helped. I had taken bottles of water for me, so that helped. Everyone was out of their cars, I sat in the shade of a bush on the embankment by the road.
Was also with DS, now older, for hours on the M6 last summer when a minibus turned over. Again we had water, healthy and nutritious snacks, he had ipod, books. People were out of cars and walking about. Needing a wee was the worst thing. Lots of people went up the embankment into bushes - I had a loose dress on and managed discreetly with a tupperware box, and DS weed in an empty bottle.
I always travel with water, good snacks, a blanket, a space blanket (for cold), torch, wipes, an actual map. In snowy weather I have been known to set off with a flask of hot drink, and in summer a cooler bag with drinks and ice packs for the food and drink.