Fell apart!

I am brand new to this site and looking for some help.  I just, sort of, finished my second sprint triathlon of the season and had similar results.  I FELL APART on the last few miles of the bike and crashed on the run.  

Background - Trained for this event pretty hard.  Lots of interval training, brick sessions, and endurance rides and runs.  Was already in good shape, even before I got into triathlons, so exercise is not new to me.  Always seem to struggle with sustained energy and endurance though.

Race - This sprint was a long one. 1/2 mile swim, 17 mile bike, 3 mile run.  Temperature was 95 degree's and very humid.  I hydrated heavily a few days before the race and carbed up the best that I could.   

 I think my biggest problem on race day was a complete FAILURE to maintain energy and hydration.  I sweat more than most people and felt energy depleted coming out of the water.  By the time I hit the bike I was sluggish, so obviously the run was a disaster.  Yeah, I swam to hard!  Only had time to drink the water bottle on my bike and down a hammer gel pack while biking.  Not nearly enough.

QUESTION - What can I do prior to, and during, the race to ensure that I have energy to burn?  Every race I've been in thus far I start cramping because I dehydrate so much faster than other people.