Hiya Frank,
There are obviously different ways to approach the flight gear issue. and Ill give a few.
My dad built a starter/flight box out of 1/8" lauan plywood. It holds a 12v battery that powers a power panel for glow ignitor and starter. It also has a top deck for tach, fuel syringe and other stuff needed to get a model started, and a pull-out drawer for basic tools, enough to tighten props, change glow plugs, and so on. Any maintenance heavier than that should be done off the field. The box is only about a cubic foot in size, so its small and light. He also has boxes for handles, props, and other tools, spare parts and so on. All of those don't necessarily need to leave the car but theyre there if needed.
I am a minimalist; I have one box and a milk crate for fuel. My box carries a few spare parts for the few models I fly, handles for those models, tools and flight equipment. I go out to the circle with a small ignitor, tach and syringe.
My best advise, because it sounds like you are looking to consolidate, is build your own box. Determine what all needs to go in it, and what functionalities it needs to perform. Then draw it out on a large piece of paper or on the back of some old plans. By making your own, it can be, hold, and do whatever you want.
I just finished building a storage and transport box for my FF gliders. Due to the shape of the models and how they break down, the box would have a lot of unused space in them, which would be kind of wasteful. I also needed a dedicated tool/equipment box, as I was doing the same thing that you described with cardboard boxes and such. What I came up with effectively kills two birds with one stone. It is also 1/8" lauan with 3/4" square pine frame. The drawers are big enough to hold everything: tools, spare parts, flight equipment, CA, epoxy, and room for much more if I need it. It is also modular and not really made for any particular type of model, so it will hold anything I build under 1m wingspan. I'm sharing this as an example. Your imagination is the limit!