Airline Travel

So we just booked a flight to travel with our 'new' baby. He'll be two months old at the time. We're renting a car and have to bring his carrier, stroller and car seat base. We're flying on an airline that allows two checked bags for no fees, so luggage will not be an issue. Also we're leaving on a Friday and coming back home on a Sunday, so it's not necessarily a long trip. Slightly freaking out because I over pack for myself and I feel that I'll be packing his entire closet! What are the necessity items for his carry-on bag that I shouldn't forget?!