First of all, you are confusing two very different snakes.
The Scarlet Snake (Cemophora coccinea) does terribly in captivity. The only way people have kept them alive for short periods was by denying them water and them feeding them egg yolks when they were dehydrated. They "drank" the egg yolks to replace the fluids they had lost. Otherwise, they appear to eat only reptile eggs and some small species lizard. AFAIK, they won't eat in captivity except under such extreme circumstances.
The Scarlet Kingsnake (Lampropeltis triangulum elapsoides) does a little better in captivity, but hardly well. It is high strung, doesn't enjoy being held (it will usually bite when restrained) and prefers to eat skinks in captivity. Adults will generally take pinkie mice, but in many cases you have to scent those pinkies with skink smell. Babies are too small to take pinkies and usually require juvenile skinks to keep them alive.
On top of that, Scarlet Kings are escape artists with few equals. If there is ANY possible way they could squeeze, climb or otherwise magically free themselves from a cage, they will do so.
Neither of these species is a good candidate for a beginning snake keeper. Frankly, neither species is really suited to captivity for even an advanced snake keeper (and I kept Scarlet Kings for a number of years).
-----
Chris Harrison
San Antonio, Texas