I played with fuel blending a while ago. Fossil fuel has 2x the BTU/lb that denatured alcohol has, roughly, so I figured if I could "sneak" some fossil fuel in with the alcohol I might get more BTUs for the weight.
I started with kerosene because it's a relatively safe fuel. I found that kero and alcohol don't mix and the result is a milky substance that makes an awful black smoky mess.
I stopped here after talking to a chemical engineering friend. She told me that to get the energy capacity of the blended fuel I would just average out the BTU/lb if the two (or more) fuels... but that I should be careful because by the time where I started to see a significant advantage to using, say, unleaded gas... well then the fuel would be very dangerous. The vapor pressures involved here are very different.
So I gave this up.
I did have a scout that use unleaded in his alcohol stove despite direct instructions not to try this (pretty much the same thing as saying, "Try this!" to a 16 year old young man.) It burned out of control and he was darn lucky not to injure himself or burn down his garage.
It might be worth playing with again but I am not sure what else to mix with Alcohol.
By the way, my CE friend told me that they mix all sorts of nasty stuff with gas and that one has to be careful if you burn unleaded fuel from the pump. I don't know about that but she is a pretty smart lady.