My 4yo DD is notoriously difficult when it comes to clothing. She will only wear short-sleeved or sleeveless dresses all year round (or skirts), so we stock up on long sleeve t-shirts. We also buy a bundle of tights (the thick cotton ones) and leggings. At least five pairs of tights. We buy the warmest pair of winter boots we can afford. We always get the girls a 3-in-1 jacket, since DD does not like the bulk of the full jacket, she can wear the liner in the car and put the shell over it when she's outside. Essentially, we just dress her for fall and put a dress or skirt over it

We can occasionally get her to wear a cardigan, so we usually have one or two of those on hand for layering. Luckily, despite being skinny as a stick, DD2 does not often get cold. I guess that comes from being born in Montana mid-winter LOL.
So I guess my absolute basics would be 5 long-sleeved shirts, 5 pairs of tights, 5 pairs of leggings, whatever summer dresses she's still attached to, a pair of boots, a 3-in-1 coat, and a sweater-cardigan or two if we can find them on sale or at the thrift store (since there's no guarantee she'll wear them!) We also keep her spring jacket on hand in case she needs another layer under her coat. I could probably get by with a little less if DD didn't insist on wearing absolutely spotless clothes, so she changes too often.
I guess it all depends on where you're living (I forgot to look). Here in Colorado, there's precious little difference between fall and winter. Also, the snow is so dry it doesn't wet you to the bone and can just be brushed off. So staying dry isn't a problem, just staying warm. We're moving to Maine in three weeks, so we'll see how our wardrobe changes when we're confronted with wet AND cold LOL!
ETA: I would have added pajamas, but both DDs refuse to wear anything but undies at night. If I had normal children, I'd get pajamas too! Probably the fleece footed one-pieces.