Frozen thawed prey should be the basic food in your captive snake's diet. Feeding frozen thawed keeps your snake from being attacked by live prey. Additionally, it is much easier to get an animal to transition for an occasional live prey feeding from frozen-thawed than it is the other way around. However, animals fed only frozen thawed might not see live prey as food. They may even become afraid of it.
Size matters when deciding what to feed a snake. For instance, If all you feed a large snake is one single frozen rat per feeding, even if you choose a large, retired breeder, it will die of starvation.
Most reptile keepers with experience in keeping snakes avoid feeding mice, unless they keep very small snakes. Mice and rats smell different to snakes and it can be very difficult to switch a snake from eating one rodent to another.
Meat eating reptiles need whole animals — the guts, the stomach, the bones, the head. Snakes are designed to eat whole animals, not butchered ones. Snakes are often prey specific and sliced meat such as lunch meat is too highly processed for their systems. They also wouldn't know where to start eating a processed or even a butchered cut of meat since they usually start by ingesting the prey head first.
Leaving food in a bowl isn't an option when feeding meat eaters. The care giver must engage the reptile's interest in the food by teasing and tempting the snake with it, except in the case of feeding live prey.
Many reptile keepers and handlers breed large prey, such as rabbits just for the purpose of feeding them to snakes and other large reptiles. Breeding and harvesting these animals is no different than breeding goldfish to feed piranhas or raising cattle for human consumption.
Some keepers feed large snakes, such as reticulated pythons and anacondas, baby pigs that have been still birthed or otherwise culled. These piglets are also frozen and then thawed for feeding.
Going to the pet store to purchase rats or rabbits is a last resort in buying food for carnivorous reptiles. Animals sold for pets are too expensive for serious reptile keepers. Pre-frozen feeder animals can be purchased in bulk for much less expense.