What do you think is the most underrated ingredient in my kitchen?

I ask you because I've only been cooking for myself for the past three months. My pantry is lacking so I think I can afford to add ingredients slowly because I live alone and I won't go broke. I don't have a lot of money and I tend to stick to ingredients that are cheap and healthy and that keep well like eggs, beans, and grains.<br><br>I run out of some ingredients eventually so I'm trying to keep a consistent inventory of my pantry, fridge and freezer. My fridge is in a tiny studio so I'm trying to make the most of it. I have a strong air conditioning unit in my room and it keeps all my ingredients fresh a lot longer. All in all, I'm trying to live a healthy lifestyle despite my financial situation. <br><br>So, I want to add at least three ingredients that I can use in more dishes. It can be a spice, a sweetener, a baking powder, a type of vinegar, some cereal, a grain, a type of flour, some seeds, a type of sauce, or anything you think I might not already have, and which will be good to have.