Dinnertime was a ritualized event as I remember it from my childhood. This was true for many more families in that era. My father sat at a particular place at our table. My mother and grandmother cooked our food from basic ingredients, often from our garden. In my particular family, children had to eat anything that was green on our plate but from that point on it was up to us to select what food we wanted until the last piece of squash or spoonful of rice or whatever was gone or put away. Salad was dished up for us and we were just expected to eat it. We drank water between meals because my parents did not believe one should drink with meals. Something about "diluting the digestive juices". I only remember fruit juice when we squeezed it out of some citrus fruit. They were also suspicious of milk so that did not appear as an option. Soda pop was evil and for corrupt and ignorant people. We ate at the same time every day altogether. I don't remember much conversation but I remember kicking my brother under the table. After dinner, kids washed the dishes. This is how it went until I suggested that I do the cooking (I was around eleven years old) and from then on my mother and I exchanged roles after meals and I was allowed to skip clean up.
I wish I could say that I continued that pattern of mealtime when I raised my children but my husband and I both worked different shifts so we did not manage to provide this much structure or this much healthy food. The best we managed in terms of a ritual mealtime was have the exact same breakfast together one weekend morning for years and throughout our marriage we have shared many, many weekend meals with family and friends. My children, all grown now, still talk about these more ritualized and social eating events. Nobody wants to remember the more typical dinners at our house. It was hit or miss over the years in terms of a family dinner together. We often let our children eat alone rather than in a family group. We ate some packaged food and my kids often indicated that they enjoyed this more than what I cooked. We did not insist on our children washing the dishes every night as they often seemed to have other more important things to do. I was the only one who cooked and everyone else assembled food. The result of our random, disorganized meal program was that I often felt like the victim of picky, bad mannered complainers at the family meals that I did make. We had the same unpleasant discussions about food a thousand times. My parents found my children's behavior to be clear evidence of our parenting failure so I erratically switched parenting strategies from 1) resignation and guilt to, 2) angry witch mother with a vague plan to teach my spoiled children to appreciate good healthy meals. I varied my parenting strategy without warning day-to-day. All that confessed, I really feel ridiculous offering advice on this topic. But, here it is anyway. Perhaps you can do better.
Mealtime with a child who has autism is apparently even more challenging than what I experienced but I think that my parents were on the right track on this thing. Ritual and routine are the solution to many problems with children who have autism (and probably other children too) and my parents created the rituals. They were not particularly creative or even interesting rituals but they were consistent and they worked. For many children, the only predictable aspect in eating is that the processed food comes in the same distinctive package and tastes exactly the same each time it is prepared. There may be some social ritual but it is not pleasant. It consists of arguing about what one will or won't eat or flat out refusing food and having anxious parents coax, beg and threaten. The mealtime rituals can be controlled easily by a child with autism and the child may feel the need to do this because the child has more than the typical amount anxiety around food with all the sensory challenges that food produces. For children with a high need for predictability,ie a child with autism, this picky, socially controlling route is way too attractive and any child with autism, given no other rituals, will create these.
It would be wise for adults to create predictable social routines around mealtime. The exact nature of the rituals probably does not matter, so long as they are consistent and recognizable to the child. It would be very helpful if a child with autism was only offered real homemade food, never processed food from distinctive and seductive packages, because given the option there is only one choice as far as the child is concerned. All children are vulnerable to packaged, processed food but children with autism are doomed. It would be wise if a child with autism had the opportunity to sit down to dinner at the same time each day because then his or her nervous system and digestive system would learn to expect food at this time. It would be wise if the whole family sat in the same places each night, said a prayer before eating and/or put a distinctive and calming bit of music before each meal thus clearly marking the start of mealtime clearly and distinctively. It would be wise if plates were dished up all the same with at least a little healthy food sitting on all the plates. It would be good if everyone ate and chatted modeling both appropriate eating and social behavior. It would be best if not much attention was given to food that was left uneaten except that no processed packaged food would be offered earlier or later to compete with the real food. It would be good if a child with autism was included in the ritual of cleaning up after dinner and when able, in the preparation of food earlier.
A positive social ritual created around mealtimes does become important to the child with autism. The families who have this kind of mealtime have children who learn to eat more foods and to eat food more happily, just as other children do. Sensory and digestion issues are part of the problem that children with autism have with eating but not the whole problem.