If a farmer's equipment is stored in an outbuilding that is in a zone requiring insurance, do we need flood insurance on the equipment? Does it matter if it can be driven off such as a tractor?

Do you have both the building and equipment as collateral? Normally, if something can move under its own power it cannot be insured under the NFIP.

You only have to require flood insurance on contents if your loan is secured by both the RE and the contents. I don't believe vehicles (things that can be driven) are considered contents though, since they are easily and quickly moveable.

The loan is secured by both real estate and a blanket lien on all farm assets. It was a workout deal from a bank we recently purchased.

"All farm assets" is pretty broad, you are going to have to determine what is in the building and what is eligible for flood insurance.