I'm not sure how my era of fandom should be classified.
I was born in November 1962 and vaguely
remember a sequence or two when the series first aired (specifically the "looming" shot of the Doomsday Machine as it slowly filled the screen accompanied by Sol Kaplan's score), but I remembered a bit more of "Lost in Space" when it still aired in prime-time.
It was actually the Fall of 1972 when I started to watch the syndicated reruns with rapt attention. And I did so initially
so I'd know what to do when my childhood buddy Kyle wanted to play "let's pretend". (Today I guess we'd call it informal "role play", no dice, no rules, just on the spot improv'.) Kyle needed a Spock to play opposite his Kirk. Since I stood an inch or two taller than he and I possessed black hair, I got the role. Within a couple of months, I watched simply because I liked it.
Come September 1973, the animated series debuted and the the affiliate stopped airing the live-action reruns during the two years TAS aired. It did not return until the Fall of 1975. (Obviously, different affiliates handled broadcasts differently, but this was the way Birmingham, Alabama did it.)
Maybe I shoule be listed as a "first rerun" fan? Maybe there's a better term.
Anyway, a lot of points have already been mentioned, but one I didn't see (unless I just overlooked the text) was the (in)famous "Exploration Set" model kit by AMT. Yeah, we may laugh at it today given we can purchase properly scaled prop/toys released through Asylum Arts at a reasonable price. But at the time, the "kid sized" field gear was the answer to a lot of prayers. Before its release, Kyle and I had to "make do" with smuggled TV remotes as pocket phasers, binocular cases as tricorders, and probably most awkward, his mother's expended make-up "compacts" for communicators. Kyle kept the black rectangular case for himself (not that I blame him), but I got stuck with a pink circular one. I rarely "hailed the ship" if we played outside lest the older kids in the apartment complex spotted me! Finally, we had pieces that actually looked (more or less) like the equipment "real" landing parties used!
I never figured out how to make acceptable ears. Today, there exists all sorts of ear tip appliances, but during my personal "heyday" spanning from 1972 to 75 (when Kyle and I both moved from the complex), decent ear props just didn't exist. No, I didn't do the "cardboard schtick"; even I was not that dorky. A local magic shop sold "elf" ears, but they slipped over the entire ear and looked clownishly oversized. One time my father and I patroned a local "celebrity themed" restaurant and I saw a waiter dressed as Spock. His ears, while not as refined as Nimoy's appliances certainly looked better than the rubber "ear muffs" I saw in the shop. He explained that he used a material called "nose putty", basically a clay-like material used to build up distinctive facial features. Later, I bought a tube, but I never could shape it as I wanted and it sure as h3ll didn't want to adhere to my ears. (In retrospect, I assumed he used additional materials like spirit gum to "glue" the putty into place.) Of course, by the time we moved apart (Kyle to a different town), my incentive to "role play" was gone.