The most basic form of this would be to simply grab a can of gasoline and spread it around but it doesn't have to be this monotonous (even though that'd still be pretty cool and should still be an option if this is even considered to be implemented) once you pick up a can of gasoline, you'll pull the cap off, after this you can just throw the damn thing and just let a neat line of gasoline drip out from the can, after which it can be shot to set fire to a wide area.
This can be considered a makeshift weapon (and be picked up like one) and it'll add some diversity to the roster of makeshift weapons we have now, which are all melee atm(at the moment)
But enough with gascans, I'm sure you've already seen One Of Those Suggetsions already, what I decided to type this out for is molotovs, specifically un-lit ones.
When switching to throw mode on a molotov you won't just throw the entire thing, instead, you'll throw a normal molotov that'll splash out tons of whiskey (or gasoline, I've no idea what's in those things) but if thrown on a player it'll make the player dripping wet with whiskey, meaning they cannot shoot or get shot until they dry off, which'll take many rolls on the ground, if they do shoot, get shot, or come in contact with fire they'll enter stage 2 fire.
Now for the gasoline itself(or whiskey), lit gasoline can't be rolled on to put off fires, actually, this'll cause you to enter level 2 fire, but if it's not lit it'll cause you to get a bit wet... literally. You perverts...
objects can also be drenched with gasoline, once lit it'll cause anyone who's taking cover on it to instantly enter stage 2 fire
Now for more optional, smaller suggestions
Gasoline on an object or a player will be highlighted like how low-durabillity objects textures are dimmed, instead, things covered in gasoline will have a yellow hue
being wet with whiskey will take actual rolls to dry off, not diving into an object without rolling because that could be exploited.
You leave a trail of gasoline while wet... again, literally. You perverts?
Off Topic
Aaaand that's about it, give me a moment to pat myself on the back for suggesting a long and elaborate idea during the most hectic part of SFD's development cycle, when the devs do not have the fucks to give to some "lvl99 suggester" and the only ones who do are kind and respectful people like Sree