I first started collecting cards at the age of 9 in 1975, but I don't remember anything about my first pack because I got into it gradually. I collected the Topps MVP set that year because I liked the pictures of old Topps cards on the fronts, presaging my interest in vintage. One of the neighbor kids stole them from me ("hocked" them, as we said), and I don't think I had them all again until I bought the 1975 Topps set about 15 years ago. I do remember that year when my dad brought home some packs of cards for me and my brother, and one of us got Jackie Brown, who had a big chaw of tobacco in his mouth on that year's card.
I bought more cards in 1976 and made a good run at the set, but didn't come close to finishing it. I also bought one Topps card from each year, 1952 to 1975, starting my collection of non-current cards. To represent 1976, I picked a random card from that year out of my collection, which turned out to be Duffy Dyer. In 1977 I decided that I was going to collect the set, and I further decided that the first card I saw in my first pack of the year was going to go into my run of consecutive years of Topps cards. That first card from that first pack of the year, which I bought at the 7-11 at Butterfield Road and Park Boulevard, was John Montefusco, which I still have. In 1978 I did the same thing, and my first card that year was Pablo Torrealba. I'm blanking right now on who my first card of 1979 was, but in 1980 it was Don Money.
Edited to add:
Here are images of those first cards I got in 1977 and 1978 (not the actual cards from my collection):
