I have not brought in full meals yet, but I have considered doing so. I usually bring in a number of snacks to have throughout the day. The meal plan does not work for me as I do not eat the way it is set up so it would be a waste of money. For me the cost is not the issue, it is the options available without having to go to three different CS or QS locations to make a meal I would actually enjoy eating.
I find most CS meals too heavy for lunch day after day. I would be happy with a rotisserie chicken wrap with a side of fresh sliced apples, carrots and celery. (I do not like the packaged apple slices or carrots that WDW gives out with kids meals.) I know that there are carts in each park where I can purchase fresh fruits and vegetables, but I am not paying to get one banana when I could get a bunch for the same price.
I usually eat my snacks while waiting for an outdoor show or parade and would likely eat my lunch in the same manner. I know that I have gotten meals in WS and ate them along the concrete walls along the water. Eating outside in the heat at WDW is no different than eating outside in the heat during a cook out or picnic anywhere else.