I was asked what do I when I plan to go on a shoot.

Here are some thoughts.

Don't forget anything.
Shutter Release - extra batteries for flashes, and cordless releases.
Lens cloths and cleaners
Tripod, Head and Plate
Memory Cards
Camera and Battery - don't laugh, last year I went on vacation and I forgot the battery on the charger.
If you think of something the night before - don't count on remembering it the next morning - get off the couch and pack it - or set it aside. I did that with my shutter release once and left it on my desk.
Have a dedicated bag for pro shoots - and don't take anything out of it - ever. Everything is always there - and stays there.
Set your camera to base ASA - and get off Auto ASA.
I shoot everything on Manual - Set it and keep it there.
If going wide - check the main element for dust - those bulbous elements, when in the sun show everything - and dust on those is the worst to try to correct in post - almost impossible.
Hoods
Do a quick check for sensor dust - it's probably too late for a deep clean but a blow may be better than nothing.
Format your memory card.
Batteries at full charge.
Know where you are going and be sure others at the site know who you are.
Bring business cards - I was carded on site by a client to prove who I was.
Don't shoot when you are hungry
Compose and frame - and take a breath - look at the scene - and then shoot. Slow down and notice the non-obvious. Gum wrappers - distractions in the frame etc.
Make sure everything is correctly framed and square - if it can be fixed in camera - do it.
Be sure you are shooting RAW.
If you can - shoot to two memory cards at once.
Slow down -- slow down - slow down.
What you miss now - may not be able to be captured at another time.