A lot of money can be saved by going to Goodwill (or any thrift store) and buying soft-sided bags...you can find some really quality stuff this way, get a little creative, and throw a little savings toward your gas tank. You can also find old Nalgene/Sigg-type bottles which can be used for fluids storage. I store my fluid containers in a rubbermaid tub, which serves double duty: it contains spills inside the truck and can be used to contain disastrous fluid leaks outside the truck, avoiding an Exxon Valdez/BP crisis in the boonies.
I was amazed when I took my craftsman socket & tool set and emptied it into a small canvas mechanic's bag. Not only did the bag end up taking 1/4 the space vs. the box, I was able to throw twice as many additional tools inside! This route tends to make less noise on bumps too. Bags compress so much better and hardly impact the overall weight of your kit. You can keep it organized by "nesting" several smaller bags of gear inside of the larger luggage style bags.
Sealline bags and other dry bags are great for clothes and sleeping bags. Only downsides: they cost more and there's a possibility of condensation building inside when there's a big temp differential.
Pelicans, Stormcases, etc are nice but I find them very heavy for my payload, not to mention my wallet. It's definitely worth the sacrifice if you want to protect an investment. We use one to protect our laptop and other fragile equipment (where you wouldn't want the compress-ability of bags). As mentioned another plus is security...however, you could achieve similar results by bolting down a simple homemade box that locks to fit all your soft-sided bags...if you haven't guessed I'm cheap and don't mind sacrificing a little bling
