Hi Ben, I'm a Newbie too. I got some food grade rectangular buckets from my local 31 Flavors ice cream store for free (they had cake frosting in them). I hear donut shops also have food grade buckets for free or cheap. I'm trying to find a cheap local source of large water containers right now.
I'm sure some "old timers" will have lots of good input.
i just use the rubbermaid totes one can pick up at target for less than $10 apiece.they are stackable and some are clear so one can see whats inside.
but for my most valuable stuff,mainly gun and survival and outdoor gear,i use the rubbermaid action totes which are sturdier and can be locked.