Plan. I bought a few newborn and 0-3 month really summer outfits at a consignment sale since Bee was a spring baby. And because they were cute. And I spend $3 on the most expensive one. That and our stock of newborn (a few) and 3 month (plently) short sleeve onesies will get us through. For Onesies I love Carters. The are really long and fit both my skinny and my chunker well. I have sleepers, pants and all the rest and we can layer when we go somewhere with AC. Chicago in September can be everything all withing a few days, so depending on the size and weather, we may dip into Bees old summer clothes in larger sizes or not.
I always skipped the mittens and brought baby nail clippers with me.
We have a few pairs of the newborn baby legs and they are great. My friends chunky daughter is still wearing the pair I sent her at 8 months.
I am mostly finished sorting the giant pile of kids/baby clothes that do not currently fit anyone. Then we will see what I really have, but I know it is enough for triplets. I love consignment sales and the one I do here has a bag sale at the end. Everything you can fit in a big blue Ikea bag for $5, and much of what is left is baby clothes. So we are well stocked.
I love the Hanna Anderson zip one pieces and always keep an eye out. I love that the cuffs look right folded up or down so they last longer.