I didn't learn any of these as a child from home. Mostly feral would be a fair description of me - especially when it came to food, as I was hungry far too often. There were enough of us to make the appearance of a meal an exercise in getting as much as possible in within as short a time as possible so we could get the hell back out of the way again without losing something of a 'high value' (like a potato) to an equally hungry sibling in the process.
However, I was lucky enough to occasionally see my grandparents and there were a few older ladies or gentlemen who did voluntary work at school/Brownies or taught particular activities. I was always fascinated by how calm, elegant and precise they seemed - and the fact they didn't appear to feel compelled to hit me across the side of the head was a significant bonus - and I must have watched, listened and absorbed a lot of these things without realising it.
Most of the food related ones seem to be about minimising the opportunities for dropping a load of it down your front, such as small pieces of bread, tilting the soup spoon away from you or guiding things onto the back of the tines - it's physics, really, as the act of bringing food towards and up creates forces that could, if strong enough, send it flying towards your front - or reducing potential contamination through double dipping, reaching over somebody else or messing about with condiments repeatedly.
I also prefer anything that means my hands are left clean (I was very aware that they were dirty as a child, but soap cost money, apparently), so eating fruit with a fork feels more pleasant to me than having sticky fingers or juice running down my chin. When I've cooked for others, I've always put condiments and seasonings on the table first because it didn't seem to make any sense to wait until somebody was served food and finally sat down to ask for something; it's more efficient to put down the cutlery/lay the table and place them then, not the other way around.
I definitely absorbed the 'say again?' and 'what?' - it was so much nicer than being too scared to say you didn't understand and getting the usual wallop across the side of the head for being stupid. Didn't dare use them at home, though - I think the wallop was used as a form of punctuation, to be honest.
With visiting/parties and guests, I never experienced those, so relied upon what I saw on TV. It didn't occur to me that I would be bringing something to take back home with me. I did like the idea of writing thank yous, as it meant having a nice pen and stationery to do so - and the number of gifts I get at my workplace now is lovely.
I'm sure my manners and etiquette still leave much to be desired, but I generally use a rule of thumb that if my mother did it, it is most likely unacceptable.