Though I’ve never had the occasion to use it (and hope I never will), I carry a Sawyer Extractor snake bite kit in my backpack whenever I’m hiking around fishing for brook trout. I am told this works to extract some quantity of venom depending on where the bite is on your body. For example, on your hands or feet it is supposed to work better than if the bite is on your calf.
However, the effectiveness of the Sawyer Extractor is somewhat debatable, and apparently one of the kit’s proponents has backtracked in the past few years on his endorsement of the product. As with almost everything on the internet, it’s hard to know what the truth is. Nevertheless…
Whether you do or do not apply a quick suction to a venomous snake bite when you are in the backcountry, the most important thing is still to get to a hospital. The only sure way to treat such a wound is to get a shot of antivenin. A little extraction, if it actually works as advertised, may buy you a small window of time to hike out of the situation and get to a hospital.