You sure don't EVER want to spill any into your car. Nasty stuff on sheet metal.
Had a friend who borrowed his Mom's Caddilliac and had two garbage cans in the back seat area flip over full of brine. It toasted the car.
You want something with caps. You can buy plastic jerry cans that fit well in vehicles and don't leak.
When I get raw sea water from the Pacific I use a pickup truck and a 55gal plastic drum. You have to be careful with large containers like a 55g. You have to fill it all the way up as half empty it will slosh dramatically. I saw a truck spin out in front of me on a country road because of two partially filled drums and it was oil - much lighter than water!
You can also check camping gear stores for collapsible carrying jugs.
Here in the UK I bought a 25-Liter (6.5 gallons) canister with DI water in it from Wilco Motosave for GBP 8.99 whereas one LFS sells similar canisters empty for GBP 7.99.