Drink approximately half of the provided two litres of saccharine salt juice along with four times as much water and repeat "I will not throw up, I will not throw up, I will not throw up" internally until I begin to believe it.When I'm trying hard not to vomit, repeating the litany against fear seems to be very effective. It kind of makes me feel like a jackass but if it works it works
Music and some sort of low-stakes game on your phone with no time constraints also helps.