Longsleeved coveralls are best but you can use clothes that can be thoroughly covered with mud, ripped, etc. without concern. Clean clothes and clean shoes to change into after, as you can't get into a car for the drive back with all that mud on you. A large trash bag to put the dirty clothes and shoes in.
Bagels are pretty indestructible.
Dried fruit works well. So do singly packaged string cheese sticks. You can hide a sandwich inside the top of your helmet. We will not be leaving the cave area for lunch so bring some with you. This is not an optional item.