this is what I do, too.
also, I pack pjs, fresh underthings; a Ziplock chargers for cell phones, cameras etc. I also tote some precut moleskin & earplugs.
I do leave all the labels on our meds both perscriptions & OTC.
I also carry a BIG purse--still fits under the seat-- with my filled qt liquids baggie (makeup plus Purell); complete make up; fanny pack/Baggalini;
all confirmation numbers for rooms, ADRs, car rental etc as well as touring plan; reading material; cell phone; camera; sunglasses;
As for layering my clothes, it's snowy/cold here in NH, too, so I'll wear a light colored cotton turtleneck (can use @ WDW if it gets chilly) under a pale yellow cotton tunic sweater topped off by an all season coat w/a zip out lining. I bring those cheap little stretchy gloves in black for everyone, too.
DH & DS usually wear heavy sweatshirts with collared polo shirts underneath & jeans.
Even if we have to wait for the airport parking lot shuttle, it's never a long wait, so we just don't put on winter coats even when it is below zero
I always make sure to check the airlines website about a month before our trip to be sure the carry on number & size limits have not changed. I check again 48 hrs before we leave.
Jean