First of all, get a higher quality sunscreen with a higher SPF, and NOT the spray crap. Certain skin type can become intolerant to low quality sunscreen, I now must depend on ensuring all my sunscreen has actual Zinc in it. Then cover it up.
Hydrate your body from the inside out. It's going to hurt, its a burn, drink as much healthy clear liquids as you can tolerate.
If you are to the point where you are depending on Tylenol to not be in pain, you may actually have sun poisoning, which I have had twice.
TEA Bath, fill a tub with luke warm water and dump a whole bunch, as many tea bags in the water as you can. Specially if you can get black tea. The tannis in tea will draw the heat out of the burn in just one bath. If you can, brew the tea extra heavy duty strong and then pour it in the bath. If you don't have a bath to use, brew the tea extra strong and soak washcloths or tea towels in the brew and very lightly drape over the skin.
(Long story short, yes, I've had to do this once, for my bonehead DH who shaves his head bare. He insisted he would be fine all day long at Blizzard Beach only putting sunscreen on twice in 10 hours, cause we're "from Florida" so he would be fine, yeah, well the rest of us we reapplying every hour. I went to the front desk and asked for 10 black tea bags to brew in the single cup Keurig and two extra washcloths)
If they are staying at a hotel, they can even get black tea bags from the front desk, almost every store sells black tea very commonly now.