I agree that carseat/stroller is awesome.I had to carry my 13mo,carseat,and huge backpack when the two of us went from Ohio to Turkey.
I remember taking snacks and drinks.Extra cloths.Playdough,bubbles,finger puppets,and .....that was it. The bubbles worked good in the airport.I also took some wipes because a recent news story found fecal residue on the headrest....so I wiped our entire area.Also some hylands vitC and echinacea drops for immue boosting.I took rescue remedy for emotional upset,but she never needed it.I might have had some hylands teething tablets.Some people let there little ones wander the aisles,but my girl only got out of her seat when she or I needed to use the bathroom.The bathroom was the worst part of the flight.
Oh and for you...something for headaches.I remember having the worst headache when we were on the 10 hour flight over the Atlantic.I had no meds and was seated next to a sick family of 5.Then there was a delay for the NY to Cleveland flight.It was a long trip home!
Once in the air see if you can move seats to an area with less people.I know we were restricted from some seats due to the carseat and in the case of emergency.I also had to ask to make sure I was able to get on every flight before the crowds so I could strap in the carseat.
We paid for a seat for my daughter too.And I agree about not stressing.I remember my dd crying on the first plane(we took 6 planes total) and luckily the guy behind us stuck his hand between the seats with a face on his hand,and made my dd laugh.You can only do so much.
We traveled in the afternoon going and coming home started in the am.The afternoon one was easier since she slept more on the ocean flight.If you can keep your little one up a bit,or wake early for travel then he might sleep better on the flight.
Enjoy your time in SC!