0-3 month all you really end up using are snap-button onesies and zip-up or velcro swaddle things. You don't need many newborn diapers. They outgrow them VERY fast. Usually size 3 and 4 are most used diapers. Also make sure to snag as many as you can of those waterproof cloth pad things from the hospital. Always stick one under the crib and wherever you change them. They're useful all the way thru potty training. Just slip one under the fitted sheet.
Bedding tip for kids beds. Use a waterproof mattress cover and top sheet then put another waterproof mattress cover and sheet on top of that. Really helpful for nighttime accidents or in case of illness. You can just take off top sheet and mattress cover and not have to worry about making the bed in the middle of the night.