It's hard to decide which one item because I always carry with me a lot of things for survival. LOL But there is one perhaps that is most important. I can't live without my anti-hypertension meds. I have bad kidneys and kidneys control blood pressure. I always carry with me 2 types of hypertension meds, one is Amlodipine 10mg for blood pressure above 140 up to 180 and another one called Clonidine for when my blood pressure spikes 180 up to beyond 200. The first one is my maintenance medication that I need to take daily and the second one is an emergency medicine, I can take it when I am having so much discomfort of having high BP already like blurred vision, headache, chest pains, and a lot more, it can be taken without water. It just needs to be placed below my tongue until it melts. I can leave the house without my celfone but I cannot leave the house without my emergency meds.