Dependent on the temperature, your water needs and the amount of bottle cages you have, you could try 1 bottle with a malto:fructose mix and 1 bottle with plain water. The bottle with the malto:fructose mix contains all your carbs for the entire ride, making it effectively a very large gel. The water bottle you can top up wherever you’re stopping.
This works for me, and I can get enough fuel for a 3hr ride in 1 large bottle. If I need extra I use a few gels or blocks.