There is no limit to the food items that you can even think of a snake might eat. Different species have different preys that they prefer to have. There are common preys that most of them like to have. According to season they might change their prey. Whatever is available in abundance would become the prey for the snakes. Depending on their growth their diet also varies. A simple search on the Internet for the phrase what do snakes eat would reveal a lot of interesting things to you. Some of the snakes prefer to have a particular prey alone. Even if there is irregular supply of prey in a particular place they could survive that condition since they are cold blooded.
Some of the snakes like the tentacles snake eat aquatic plants apart from eating fish. Do not think that a snake might catch any prey that passes it. They would evaluate the prey they are planning to catch. If the prey is too small for it to be the meal then it might not even consider hunting. Some of the prey might be bigger for them to swallow. So they might even pass it without attacking it. Rodents serve as the important prey for most of the snakes. Note that it is a mammal. Snakes use their venom and constriction to kill the mammals and this method is well suited to kill the mammals before they eat. That could be one of the reasons for them to eat mammals mostly.
The other food that they prefer to have is other snakes. It is easy to swallow other snakes since they easily fit their long body. For example the King Snake will eat snakes like rattlesnake by constricting them before eating. They also have other prey other than snakes. It is a wonder that some of the snakes that eat other snakes are harmless. One of the other snakes that also prey on snakes is the King Cobra.
There are snakes that are considered snail specialists. They eat snails tactically without eating the shell. Snakes like the Brown snake, the thirst snake, and the Southeast Asian Snail eating snakes use different methods to extract the snail from the shell so that they can eat more snails without eating the shells.
On searching the web for some more content on what do snakes eat you might wonder when you come across other weird things that snakes eat. Centipedes, Ants, termites, Crabs, Toads, crayfish, spiders, carrion, grasshoppers, and skinks are some of the weird items that the snakes eat. Some of the snakes are good in eating the eggs of fish, reptiles, and frogs. Snakes also drink water from the pools, ponds, and the dewdrops using their split tongue.