For the most bang for your buck, I recommend you go to a local farm store and ask about potable water tanks. Most will have the white storage tanks on an outside lot, but those aren't what you want. You want the black plastic version. The reason being that the white tanks let light in, so bacteria can grow in them. The black tanks on the other hand are built specifically for potable water. Most stores, at least in my area, won't keep them in stock since there isn't much call for them most of the time, but you can still order them. At least I know you can through Tractor Supply Company. For the same $80 you're spending on a 5 gal can, you can get a 30 or 40 gal tank and you can build your own plumbing fittings to go with it. When I worked for TSC, I helped several customers build potable water systems for cabins that weren't connected to local water sources and didn't have well access. They're pretty durable and lightweight when empty, and most portable sizes will usually come with some sort of molded features that make strapping or tying them down easy. The simplest way you can go is get a tank, set it in the back of your vehicle and hook up a hose and spigot end to the drain and you'll be all set. No muss, no fuss. Plus, the top openings are usually about 8 inches in diameter so cleaning them out is as simple as taking a rag and wiping down the inside. The lids are designed to not hold pressure, so gravity feed is the easiest way to go, but you can still seal the pressure relief valve built into the fill caps and rig up a pressure fitting if you felt you absolutely had to.
Just my 2 cents.