Sounds as if you have things under control as far as 2 liters water and one sports bottle with a rehydration mix. What kind of temps are you talking about--80's 90's?

I did post some information/research on rehydration here on TE recently/last 2 weeks...can't exactly tell you which thread, but it was recent. There are stats on how/when to rehydrate. I suggest that you go through and find the post because there were several threads addressing this exact subject. I think you will find it helpful.
Terry