Since we don't have a dealer close to here, I keep many parts. Sometime provide (don't sell them) to my friends who needs them and they order me replacements. This way we are back in the air within days.
That is what I have been doing here. We have a pseudo dealer but he only orders parts when people need them. Typically not before the fact. I loan parts and get them to replace back to my STOCK! At last check I had over $1000 retail in parts not including blades....
I have my smaller parts in four stackable Stanley parts containers (see photo). The are available at Lowes and Home Depot. Each one has certain aspects of the heli. One for bearings and gears. One for tail parts. One for frame parts, small misc hardware and skid nuts,etc. Another for head parts and all of the various shafts.
For the main gears, Skid tubes and landing gear I have a tupperware tall container with a handled lid.
For long items I tried the long thin tupperware tote but it was much larger than needed. I now just use one of the shipping boxes the blades come in. Takes up less space in my truck as I carry most of my spares to the field with me.