I got this information directly off of the NC ABC website
HERE.
Looks like 4L is the correct answer. Assuming a regular bottle is about 750ml that means you can legally purchase up to five normal sized bottles and bring them across the state line. I don't see anything about a time period so i guess you can make as many trips as you want in a day as long as you only bring across what is allowed.
Also unlimited kegs!
Q: How much alcoholic beverages can I buy and transport?
A: North Carolina State law allows the following amounts of beer and unfortified wine to be purchased and transported without a
permit:
BEER – Maximum of 80 liters I cans or bottles
(9) cases and (9) cans/bottles – 355 milliliter (12 oz)
(7) cases and (1) can/bottle – 473 milliliter (16 oz)
Kegs – unlimited
UNFORTIFIED WINE – Maximum of 50 liters
(10) 5 liter containers
(66) 750 milliliter bottles
(50) 1 liter bottles
(28) 1.75 liter bottles
SPIRITUOUS LIQUOR AND FORTIFIED WINE – 8 liters
COMBINATION OF SPIRITUOUS LIQUOR AND FORTIFIED WINE – 8 liters maximum
A person may only bring into the state 4 liters of fortified wine or spirituous liquor or a combination of the two.
A maximum of 100 liters of unfortified wine may be transported with a Purchase-Transportation permit. These free permits are issued by your local
ABC store.