This isn't a massive deal at all, but the situation is this. My brother has a two-year-old child with an ex-girlfriend. They broke up before the baby was even born and now it's all very amicable.
Once a week, everyone is invited round to my parents' house for a meal. This includes me, my brother, my sister, the ex-girlfriend, the two-year-old and one or two friends of the family. It's very casual and laid-back- people dish up their own food, we drink lots of wine and enjoy fab cooking. Everyone enjoys it, including my ex-sister-in-law. Someone always gives my nephew a bath and gets him into his pyjamas, and (as she can't drive) someone always gives my brother's ex-girlfriend and his son a lift back to their flat.
Here's the thing. Everyone who turns up normally brings my parents an offering for the meal. This varies from a bottle of wine to some crisps or some hummus or some muddy leeks from the garden. Now obviously, if you invite someone for dinner you shouldn't expect them to provide the ingredients, but I cannot help but notice that my ex-sister-in-law has never once even made a token offering to my parents for providing regular, delicious cooking and copious amounts of alcohol. I just find this odd, as I was under the impression that it was polite to make this gesture if you were a guest for a meal.
My ex-sister in law is a lovely person who is doing an excellent job of raising my nephew and is still very much part of our family, so this isn't a personal vendetta at all, but more of an etiquette question. Is it correct to make a token offering if you are invited to eat at someone else's house, or this this an old-fashioned view?