I’ve had good luck with those clear party drink cups. They come in all sizes. It’s easy to tell when they need watering too.
I never thought of it before, but it would be easy to make vent hats from some ziploc plastic bags.
I save coffee creamer and coffee containers but I wouldn’t mind trying a little market gardening so I figured I’d get some standard/commercial stuff. I also like mixed baby greens salads and it takes a lot of baby plants to make lots of salads. I’m sure I’ll use saved containers for re-potting in something bigger.