long training day nutrition
Basically, when you sweat, you are losing more than just water. You are losing a LOT of salt, and potassium and other things that are often found in gels.
For me, I find that I don't need extra salt tabs as long as I use the PowerBar gels with the 4x sodum in them. It kind of comes down to how much you sweat, and how salty your sweat is.
They carbs that you are talking about are complex vs. simple carbs. The most typical complex carb found in gels (GU) is MALTODEXTRIN. This is often mixed with Glucose or Sucrose (simple carbs) to help your body absorb the carbohydrates more quickly. I don't like to think of them as good/bad carbs when it comes to "in-activity" nutrition. All that consuming a simple carb means is that your body is going to use that energy before it burns any fat.
Granola bars are fine as long as you can handle them, but, again, if you sweat a lot you are going to want to think about replacing some electrolytes. Maybe think about washing that granola bar down with some E-caps...
Get Chris Carmichael's book "Food for Fitness". It covers the macro nutrients (Carbs, Protein, Fat) hydration, sodium, vitamins and discusses how important timing is. How much to eat X hours prior to, during and post training/ race. I learned a lot from his book.

can someone please explain the basics of replacing things other than water and calories during a long training day. I know i need carbs (the good kind, not fructose but malodextrose?) and whatever else i get from gu. i also eat granola bars for calories. i've stareted to add long days to my training (3 hrs +) and think i need to do someting about salt? thanks for the help!