Do not write on the cave walls. When one name appears, others are tempted to do likewise. This can shortly get out of control and I urge you to subdue the impulse. Refuse of any kind should be taken out of the cave. )
Indiscriminate collecting of cave formations (speleothems) is illegal. This form of vandalism can never be repaired. Even broken speleothems should not be collected but placed to the side of the passage where they will be safe. Such formations can provide valuable information to geologists studying the cave. The only exception to collecting formations is in caves being destroyed by quarrying or road work. However, such caves can be highly dangerous and should only be visited by experienced cavers with the permission of the contractor.
Never collect fauna (bats, salamanders, fish, etc.) unless you are associated with a worthy scientific endeavor. Collecting can, and has, wiped out colonies of rare and interesting cave animals. It is hard enough for them to live as it is without you picking on them. Spent carbide is particularly destructive to water life. Hibernating bats must not be disturbed; many die when they are awakened.