Which item must be secured separately in 5-gallon cans when preparing vehicles?

When preparing vehicles for an amphibious operation, it is crucial to secure fuel and lubricants separately in 5-gallon cans. This practice is essential for several reasons. First, the transportation of fuel and lubricants in designated containers ensures compliance with safety regulations, reducing the risk of spills or leaks that could lead to fire hazards. Proper containment helps prevent contamination of other supplies and maintains the integrity of the operational environment.

Furthermore, separating these items allows for easier access during the embarkation process and ensures that they are readily available when needed. Efficient handling of fuel and lubricants is critical for maintenance and operational readiness, as they are vital to the functioning of vehicles and equipment.

In contrast, food supplies, spare parts, and tools do not require the same level of careful management in terms of containment and safety as fuel does, thus making fuel and lubricants the correct answer in this context.