I just attended a tech round-table discussion (construction safety) that briefly covered an iPhone app called iTriage. Never used it personally, but the one feature that struck a chord was that in addition to first aid, it also provided nearest hospital locations which would satisfy "the axiom is that the best field treatment for snake bites is a set of car keys and a Google map to the nearest hospital."
Out here you see a few of these. This guy was just a baby, not much more than a foot long. He was just sunning himself on the trail. Avery (my Brittany) just walked right over him and he didn't move. I chased him well off the trail and was on my way. (It is good to have a long lens on the camera!)
This guy was 5 ft long and had no rattles. There was a raw patch on the end of the tail. Looks like they got tore off somehow. I stomped on the ground a couple times and he slithered off into the grass where he coiled up and stared at me with his blue tongue testing the air.
I wouldn't put any kind of constriction on an extremity that had been bitten by a rattlesnake or any other pit viper. Sometimes the swelling of the tissue becomes so bad doctors have to perform a fasciotomy. The skin itself becomes so taut it prevents blood from flowing into the affected limb. Then bad things happen like compartment syndrome and gangrene. Check out this guy's story and his pictures: