Having a packed lunch at school. All my friends had packed lunches, whereas I got free school meals so always had school dinners.
Also eating at a restaurant that wasn't McDonalds (or equivalent)
I was always flabbergasted when school friends said they had been out for a sit down meal with their family. That was SO posh to me.
My immediate family never went out for a sit down meal together until I graduated from University.
I remember feeling very posh going to Harvester with friends for my 15th Birthday 