I remember the Scholastic book orders quite fondly, but those came through the school, not through the mail.
Other than that, the main mail I remember getting as a child was magazines, which were always fun to receive.
Yeah I remember getting those through school as well (when the child support checks were coming in).
I don’t think it was a lot. I didn’t order books through the mail because they got delivered through school. I got some sort of monthly package from National Geographic as a birthday gift from one of my uncles and maybe a magazine or two. The only people who would have given me birthday cards/checks lived close enough to give them to me in person.
As an aside, when I was in university I sent a letter to the government of Vanuatu asking what their bond rates were (on a whim). They sent me a financial statement of some sort. It was kind of neat receiving mail from the govt of Vanuatu!
OMG, I can’t believe I forgot QSR cards from amateur radio and shortwave listening. Got my novice license at around age 12-13 since my dad was also a ham. Got into shortwave listening around the same time.