There should be a tool that does the opposite of what the delete fields tool does. Instead of specifying which fields you would like to delete, you would specify which fields you would like to keep and then the tool would delete any extra fields. This would be useful when writing models where you don't always know what all of your input fields will be but you do know which fields you need to keep. I run into this problem all of the time when building models since my inputs are always changing.
