Train your dog to drink out of a water bottle is good, but I also have a bottle with a little dish built into the lid. Pop the top open, pour water into the self contained little dish. Anything the dog doesn’t drink goes back into the bottle. Less waste and less weight for us old farts to carry! Use it in the Arizona heat all the time.
Some say a dark colored dog absorbs heat from the sun more than light colored ones, but a lot of dog trainers and vets dispute that.
Chocolate sensitivity varies from species to species but generally is not good in any case! Grapes, onions, garlic, macadamia nuts, etc.
A tiny pinch of plain old salt in water is adequate, just don’t overdo it. Salty dog treats or small amounts of dog food help too, but not too much before running them or you risk gastric torsion!
Above all, condition your dog well before the season, like we all should be doing to ourselves! It’s not just dogs that drop dead on the opener!!