Whew, this is a tough one without knowing the location, the desired look, and the time of day.
Did the designer or fashion director give specific instructions for your lighting, or are you assuming that "big, even lighting" is what you want? Find some mood board or reference images that the designer likes.
For outdoors, keep the off-camera lighting simple, and just use it to complement sunlight. During most of the day, it's going to be hard to combat daylight (especially direct sun) with just a couple of Speedlights. You can wait until late afternoon, but that ol' golden hour goes by FAST - too fast to try to work with two big modifiers, and any wardrobe change will be right out. You might have time for two lighting looks, but no significant wardrobe change.
You might not even need off-camera light if the ambient plays nice, or you're in a good location with diffuse shade. I'm bad at this too - I take my Speedlights everywhere, but working outdoors I can often get better results if I just put the lights away and look for good ambient. It's hard to change that mindset... I really need to remind myself that I can get good results with ambient if I just look for it.
Edit - last time I was in a Calvin Klein store, the in-store print artwork (photos of guys in suits, blown up to big prints on the walls) were obviously done with a single hard light. Maybe late-afternoon sunlight, edited with a neutral-cool white balance, or maybe studio with one powerful light without a big soft modifier.