Over the years I have tried a few of the assortment offerings and though they do have a lot of stuff in the boxes I find half of it you will never use. I found it was better to assemble your own using the fishing organizers from places like Bass Pro Shops. For my regular parts I purchased two Bass Pro Shop tackle organizers each came with 4 snap lid boxes. One set for standard and the other for metric and nylon. I filled the boxes with sizes I found I used. When I leave for an event I just pick up the two bags and I have all my fasteners with me in case I need them.
I have 4 of the same size tackle organizers inside the top of my tool box. These are filled with all my spare engine parts. Every gas carb has a complete gasket set. Every nitro engine has gaskets and sometimes spare needle valves, prop washers and prop nuts. I have plenty of glo plugs and spare spark plugs. Even a few Walbro carb float gauges.
When I started with electrics I found everything very specific for each size motor so I used small versions of the tackle organizer for individual planes. I label the box and fill it with parts, nuts and bolts etc specific to that model. If I misplace a wing bolt no need to sort through the big boxes because I will have put a few in the little poverty pack as I call them.
Lately I have found a small box I really like and am in the process of switching all my small containers over.
First three pictures are the Bass Pro Shop cases and assortment boxes bought on sale for $15 each.
Second two pics engine spares in my main tool box.
Last picture shows the size of my first boxes and the bigger latest boxes I will be changing too. All of my glider spares fit in one box. I have an Edge and MXS from Extreme Flight and one box holds all the spares. Most of my other planes have they're own box.