We are planning a long ride this weekend and I need some advice. We will be riding approximately 120 miles. my group will be riding an 05 700 Suzuki King quad, an 03 yamaha 350 Warrior, and an 06 Yamaha 250 Bruin. We ride conservatively as we are old enough to appreciate the great Oregon Cascades scenery. So how much extra fuel should I carry to make sure we all get back safely.

 

I would bring two full gas tanks with you, that should be enough for a whole day.

 

My 350 Bruin/Grizzly can only do 68-75 miles on its small 3.8 gal gas tank. I carry a extra 2-1/2 gas can and can go 120 miles. I find lugging a 5 gallon gas can to big clumsy unless your doing a 200 mile ride.
My 500 does 100 miles to a tank and needs no extra gas carried usually with its large 5.25 gal tank ,it all depends on the ATV's gas tank size. Safely count that a ATV gets 18mpg in general but lots of times I get 20 mpg.

A warrior with a 2.5 gal tank is sure not meant for long distance cruising. Even your 700 has only a 4.6gal tank that good for about 85 miles tops.