I do serve all meals and snacks. But I have my own two children that I am already making food for. Because of that, I feel it is easier to make one meal or snack for everyone, rather than make my children food plus serve up individual meals to the dcks. If I didn't have to provide meals for my own kids, for example once they are in grade school, I would consider having children provide their own food.
My main concerns with having parents provide their own food are the nutritional value of the foods being provided, problems with kids wanting what other kids have, and dealing with containers, etc that have to be sent home every day. Also sometimes we have picnic snacks and lunches at the park spur of the moment and might be trickier depending on what parents sent. Not insurmountable problems but would require some good communication with parents to set up guidelines.