Were these definitely United flights? The FAA has minimum emergency medical kit (EMK) requirements which must include oropharyngeal airways, self inflating respiratory device with mask and IV tubing with normal saline. There is a printed sheet in the kit which lists all its contents so worth glancing through to see what is available and then can start looking for it knowing it has to be somewhere. I find it hard to believe that United is flying planes without airway equipment and IV fluids as that will be falling foul of FAA regulations. I would assume that any time an EMK is opened then the other contents are discarded or it is restocked to meet requirements so there shouldn't have been a scenario where there was no IV fluid or ambu bag unless a prior emergency in same flight.