For some stuff that doesn't fit into a box (like a spare trolling motor), I use big, heavy duffel bags. They make them with pockets that are really neat. You can put everything together in one place.
Rods are a special issue. The big thing with them is to keep them separated and straight. I like soft cases, but the hard ones are OK, too. Put something between them so they don’t rub together and make sure they are lying perfectly straight. If they’re bent and it gets real hot they’ll take that bend and you’ll never get it out. Your rod will be ruined.
I like to carry my rods in the rod locker in my boat. There’s less chance of damage that way. And, when I get to where I’m going, I carry them into my room. I don’t like to take any chances.
Plastics can be another problem. Make sure you pack them perfectly straight and that you don’t mix colors or brands. I use Plano boxes and then put foam on top of them to take up any extra space. That’ll keep them from moving around during my trip.
I always pack my line in the center of my vehicle’s storage space and at the lowest point. That’s the coolest place. When I get to where I’m going, or if I’m going to be away from it for a while, I carry my line box with me. Heat and sunlight will make it weak. You’ll break off when a big fish gets hooked. If it ever gets about 110 degrees it’s probably ruined.
When I’ve got all my tackle the way I want it, I put a couple of futon mattresses around everything. I like the ones that are three or four inches thick. They’re really useful when you’re traveling. You can sleep on them if you get tired and they make great insulation.
The last thing we need to talk about is safety. Just before you leave you should put a big cargo net over everything and make sure nothing is packed above the back of your seat. If you have a bad wreck or turn upside down you could be killed by all that stuff coming forward.