I am consistent on my exercise regime. I also take an early high carbohydrate meal before my ride. I work on my endurance months before my race and all these help to build my stamina. During my race, I do have my intermittent glucose intake.
When it comes to building stamina, nothing comes close to the good old fashion running. Start Jogging and you would automatically increase your stamina. No other activity increases your stamina as well as jogging. That’s why boxers concentrate so much on running.