Maybe try and get a hold of some empty water bubbler (water cooler) containers, they hold about 5 gallons and usually have a removable lid. I use HDPE carboys (lab stuff) that hold about the same amount and have handles, a spigot and a screw on cap. They are expensive, though, so unless you can get some cheaply, and that have not been contaminated with some weird chemical they're probably not an option.
A new, clean, plastic trash can with a lid should do fine as well, if you need larger quantities. Thoroughly rinse it (no soap) before use. Make sure it has not been treated to block odors or anything like that.
Coolers are probably OK, but they aren't really designed to be completely full of liquid, and may crack or break, and since most have some kind of foam insulation, a crack could mean contamination.