This is a topic to get great feedback on.
I looked to my local Home Depot to get two different types of heavy duty plastic tool boxes by Flambeau. The interiors differ as I wanted two types of kits, both ready to take with me in the event I had to leave home in a hurry; all kinds of crazy things happen in So. Cal.
The first kit has some pop out trays and holds basic first aid items, band aids, medicines, tweezers, thermometer, book, etc.
The second kit I consider to be more of a trauma pack and is no more than a larger tool box and holds heavy duty items; larger military dressings, gauze, SAM splints, chemical ice bags, etc.
When going camping with a large group or on a road trip, I tend to take both kits with me. I am amazed at the number of people who consider themselves to be seasoned campers who do not plan properly for an effective first aid kit, as well as those who carry nothing in their cars.
Depending on how extravagant you want to be, Tupper Ware type containers work well, keep things dry and organized.