Heres a quick note that all photographers should remember:
Not only should you tell your athlete/friend/family/model (whoever you want to impress) how heavy your backpack is, you should also have them pick it up and see for themselves. This makes you look like the badass you truly are for carrying it around. Maybe tell them about the time you crossed the entire Gobi desert carrying it, with only one bottle of water, and a small bag of trail mix with no problems. Any variations will suffice, and can only impress. Laughter will help set the tone of a shoot, and loosen up the models. Anything funny or just ridiculous (though the Gobi story is %100 true, trust me.) will be a huge help on a shoot.