Honestly, I would suggest spending the extra cash on the Canon BG-E14 Battery Grip. I know the price tag hurts, but since you have a big outdoor shoot coming up, you really dont want to risk it. Third-party options like the Vello BG-C12 Battery Grip for Canon 70D, 80D, and 90D are okay for indoor stuff, but they usually lack the same weather sealing and rigid build. Be careful with those cheaper ones because the buttons might feel mushy or the connection can drop when you're moving around. If it gets dusty or damp outside, the Canon seal is gonna protect your camera better. Make sure to test whatever you buy before Sunday tho. Better to be safe than have your gear fail mid-shoot because of a cheap accessory... splurge now so you dont regret it later.

I saw this earlier today but just now getting a chance to reply. Honestly, I have been super satisfied using third-party grips for years now and never really had any major complaints. If the Canon price tag is making you sweat, you should look at these instead:

• Meike MK-70D Battery Grip for Canon EOS 70D 80D 90D is a really solid alternative. The rubber grip texture matches the camera body almost perfectly, which is a nice touch.
• Neewer Vertical Battery Grip for Canon EOS 90D 80D 70D is basically the budget standard. It works well and I have used their grips on multiple shoots without the electronics acting up. Technically, the big thing you pay for with official gear is the weather sealing. If you arent expecting a total downpour on Sunday, save the cash. The buttons on these feel fine and they definitely wont just fall apart on you ... been there, done that.

Like someone mentioned, the price is steep, but I have to disagree about going third-party for a big outdoor gig. I once bought a cheap grip for a landscape trip and it felt so flimsy... like the plastic was gonna crack. It kept losing connection too which was a total nightmare. Honestly, just stick with the official Canon brand to be safe. You dont want equipment failure ruining your shoot.