Hope you are enjoying your vacation.* Digging plants from the wild is a big 'NO, NO' unless they aren't native plants. In most places it's illegal to do so.* If you can get seeds that would be ok.* It would be best to take photos and then we can try and search to id the particular cactus you found so we can try and id it to see if it's a native or you can purchase seeds or plants that have been cultivated without taking from the wild.
There are 3 native cactus in North Carolina.*
Cocklebur prickly pear aka Opuntia pusilla
Dwarf prickly pear aka Opuntia humifusa
Opuntia dilenii is the largest and is very rare.
You might find this article from North Carolina State University helpful.
Info about digging from the wild.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.