Enter beta-alanine, a precursor to carnosine. When you supplement with beta-alanine, you're essentially giving your body the compounds it needs to increase levels of carnosine, ultimately helping delay fatigue. That said, there haven't been as many studies supporting its long-term safety, so while it appears to improve exertion and fatigue, use caution if you plan on taking it for an extended period of time.
You can take beta-alanine at any point throughout the day, but Kendall recommends taking a total of 3 to 6g a day, separated into multiple doses of 800mg. This method "reduces the effects of paresthesia, a temporary tingling or numbness akin to when a limb falls asleep."
Caffeine has been around for centuries as a performance enhancer, so whatever your feelings about coffee are, you can rest assured that it's safe. Kendall points to the many, many years' worth of research backing the positive performance benefits of caffeine on endurance and high-intensity activity. Specifically, "Caffeine has been shown to decrease rates of fatigue and lower perception of effort, which may be of benefit during high-intensity, high-volume workouts, or if you just need a little pick-me-up before hitting the weights."