Pikachu
Zapdos
Articuno
Charizard
Blastoise
Venusaur
While I am not so sure of Blastoise (and Venusaur, kinda), I am fairly certain of Charizard being there. Can't forget how much I regret replacing Fire Blast with Fire Spin, and how I trained Venusaur all the way to lv33 in Diglett's Cave alone. Blastoise might've been Lapras instead, since I do recall training my first lapras at Cinnabar Island, before facing Blaine. It was Lv15 but swooped butt even until I reached Blaine himself, KO'ing Arcanine with Sing and a bunch of SURFs.
I remember having trained a Butterfree, mankey, krabby, snorlax, Haunter (caught as one), Sandshrew, Magikarp (yeah, the 500 pokedollar one, which i got tired of training), Jigglypuff, spearow, Nidoran M, Flareon, Pidgeot, and Dugtrio. It was a huge pain trying to get my first Bulbasaur. God. I just had to say that.
One of the first teams I also recall just as clearly was from some 12 or 13 years ago. We just moved to our new house, and my sister and I were basically tasked to watch the house while my mom and dad were picking up the remaining boxes at the old one. We then played thru yellow together. I took over only around Silph co. She loved Mankey and Haunter, so we had it til the League. I took Jolteon for our Eevee, while still keeping Pikachu. Lapras was the fifth, our surfer, and I'm not so sure if we had a sixth - Since I recall that we were struggling by the time we battled Agatha. Might've been Pidgeot, if anything,