5 gallon standard glass tank. Tetras, etc. usually. I think unfortunately at one point I had 2 Firemouths in that little thing as well, I was a pretty young kid at the time.
My first tank was a 10 gallon acrylic tank with a terribly designed built-in UGF stocked with an oranda, a waterdog (larval tiger salamander), a betta (aka waterdog snack), and a figure 8 puffer. That did NOT turn out well. lol
Before that I had a cup with a betta when I was about 2 and then a few years later a crayola crayon "tank" that held a couple gallons which I stocked with first 7 comets and later an albino ACF (who grew so big he got stuck between the UGF uplift tube and the side and drowned), but I don't count those as tanks
20 gallon with a bala shark, 2 gouramis, and a red tail shark. rocked the package deal that i got from petsmart. unfortunately non of those fish made... the bala shark almost til he bailed out of a bucket whikle moving him and my dog put a hole in him... whoops
A used 2 gallon and "used" guppies I got from my great aunt. She kept a 40 gallon in her greenhouse. It was full of anacharis and guppies. When she gave them to me it was winter and the fish were almost frozen! There was ice on the top of the tank! She just told me to keep the bag of fish in my hands and they would warm up and be OK. They were! Guppies are extremely hardy. At least the ones I had back then!