The key is to start hydrating the day before then maintain the day of. Just water, no Gatorade or sports drinks.
I have a bad habit of eating 2 burgers for lunch and then chase it with a stogie. I feel tired but my fastest session is usually right after lunch. Odd.
Bumming isn't a bad thing...it helps to pre-arrange things. I bring tools, my buddies bring drinks and other stuff. It works out.
2013 F30 328i Melbourne Red
2011 E90 M3 Monte Carlo Blue
2004 E46 M3 Imola Red