As far as a simple parts box...I got this okeechobee bag over ten years ago. It holds 8 nice sized trays. It has a big pocket on either side and a small pocket up front. Its fabric with a rubber/vinyl bottom. After all these years it still looks brand new except the zipper failed. I can get it zipped up but it just pops open. The handles have velcro so it keeps it closed.

When its fully loaded its heavy but you can walk into a clients home and have every little part you need. I use it primarily for service calls. At a new installation i just bring boxes of new parts. No point in emptying the parts box just to load it back up. After a new installation i sort the remaining parts into my okeechobee.

Its between $40-70 online depending on how many boxes you get inside it. NOTE: if you get one do not believe the dimensions. Mine is almost 20" wide. The specs online show it at 16. Amazon has it at $67 for the 8 box version. Walmart has it for $50 i think. [Link: amazon.com]