You can buy pre-sterilized agar plates, but usually just spraying them with alcohol and letting them dry works fine. It’s not technically sterile but usually doesn’t yield any problems. Alternatively, I’ve seen people using really tiny mason jars and sterilizing them with the agar already poured.
I made all of my son's purees when he was a baby, and currently I make him pouches that he can carry around and snack on.
I've frozen both the purees and the pouches. When I did purees, I froze them in small mason jars because they were the perfect size and now that my son is older I actually use them to hold sprinkles in my pantry! I have a large collection so it worked out great.
Anyways, the only foods I didn't like to freeze were actually bananas and avocado. They start to get brown so fast! But otherwise we loved everything else, blueberries, strawberries, spinach, sweet potato, all kinds of stuff.
Small Mason jars. Uniform, never going to be discontinued, and the lids are interchangeable, between 4 and 6 oz jars