This is covered in the Fluid Management section of CPNE Online Workshop Videos....
Usually the tray is sitting there in the morning for you to take credit of the fluids. Some students have had to go and get the tray back from the hallway cart to count it. Some students have been lucky when they haven't found the tray on the floor or the dirty utility area etc.
So what usually happens is... if the breakfast tray is still sitting in the room, chances are no one has taken credit for that fluid. Otherwise who ever took the tray away also records the I&O. Sometimes the CEs have told the CNAs not to take the tray so you can measure the I&O. Sometimes the CEs are more than willing to give you direction if you ask them non-content related questions.
The same goes for the urine hat. If the urine is still there, chances are no one has counted it. If they had, that staff would have emptied it to make it available for next use.