Cloth diapers. I used prefolds with my firstborn, and once he started solid foods, I didn't exactly love it, but was determined to continue to reap the financial, health, and environmental rewards.
Then when my second child was a couple months old (and wearing the same diapers her older brother had used), a friend gave me 18 Motherease one-size diapers. She had received them from a friend who used them with her only child, then my friend used them with her two girls before passing them along to me. I used them with my daughter.
And with her 3 younger siblings.
By that time, they were wearing a bit thin, and weren't really absorbent enough for my growing boy. But they were still in great shape.....so I bought new diapers and passed the MEOS' on to my friend, to use with her newborn who didn't need much absorbency. Now she has bought new doublers for them and is still using them! And I made her promise that she'll give give 'em back to me if I ever have another newborn!
This stack of diapers has a history--almost a legacy! They have helped 4 mothers diaper 8 babies from birth to toddlerhood, and still going strong! How much money--how much square footage in the landfill--have we saved? I'm sure a calculation could be done, but for me the answer is simple & doesn't require a calculator: priceless!