Okay semi serious post as I find it hard to take the topic of erections seriously.
Firstly something needs to initiate the process, whether it's a naughty thought or visual/sensual/auditory stimulation. The brain now switches off all common sense and higher reasoning and transfers control to the little brain which diverts blood to the penis faster it can drain away "et voila" an erection. A number of things can affect with the process, low blood pressure for one. Imagine your dick is like a car tyre designed to run at 35 psi but you can only get 20 psi in it. It's going to be a bit soft and squidgy. This is why some of the ED remedies use vacuum pumps. Being dehydrated can cause blood pressure to be low so being well hydrated will be beneficial. Stimulants can increase heart rate and blood pressure, back to the tyre analogy becareful not to overinflate too much it might just go "POP".
Now energy drinks may help a little in that the liquid contained will aid hydration and if they contain stimulants it's a bit of a bonus but the sugar of what ever discription (fructose,glucose, sucrose etc) will have no effect on the erection, it just means you can keep your arse bobbing up and down like a Singer sewing machine that little bit longer. Alcohol is best avoided, okay I know people like to be relaxed but you can be too relaxed and alcohol is a depressant, having said that have you seen the numbers of couples shagging round the back of the local on a Saturday night, it's shocking.
Pharmacuticals ie that little blue pill, go talk to a pharmasist.