Congrats on the upgrade! If you want reliability, dont skimp on the media. I always use SanDisk Extreme Pro 128GB UHS-II V90 cards to handle that burst rate without errors. For power, I highly recommend sticking with the official Canon LP-E6NH Lithium-Ion Battery Pack. Third-party ones can be hit or miss with the high-speed modes, and honestly, its not worth the risk for your new body.

Just catching up on this thread now. Congrats on the R6, it really is a beast compared to the old DSLRs. Since you're transitioning from the 80D, the most important thing to understand is that mirrorless bodies are basically mini-computers, so they eat power way faster than what you're used to. Regarding the cards, if you want a solid middle ground that wont break the bank, look at the Lexar Professional 1667x SDXC UHS-II 128GB. I've used these for years and they handle the R6's 20fps electronic burst surprisingly well without clogging the buffer too often. If you're ever in doubt about speeds, definitely check out a site called Camera Memory Speed. They run actual benchmarks on the R6 so you can see exactly how many shots you get before the camera slows down. It's an awesome resource for avoiding overpriced media. For the strap, I'd highly recommend the Peak Design Slide Camera Strap. The stock Canon neck strap is pretty uncomfortable for full-frame setups once you add a heavy lens. The PD system uses these little anchors so you can pop the strap off in two seconds when you're using a tripod or just want it out of the way. About the grip... the Canon BG-R10 Battery Grip is great for ergonomics if you have big hands or shoot portraits, but it adds a lot of weight. If cost is a concern, just grab a PD-compatible power bank like the Anker 737 Power Bank PowerCore 24K. The R6 supports internal charging via USB-C, so you can top off your battery during a break without needing to carry five spares.

Congrats on the R6! I moved from an 80D as well and the difference is night and day. Tbh you dont have to spend a fortune on every single accessory to get the most out of it. For cards, ProGrade Digital SDXC UHS-II V60 Gold is the sweet spot for me. It is fast enough for the R6 burst rate in most scenarios without the insane V90 price tag. Regarding the battery situation, check out the SmallRig LP-E6NH USB-C Rechargeable Camera Battery. They have a built-in USB-C port so you can charge them directly with a phone cable or power bank, which is super handy and way cheaper than buying the official Canon ones. I personally think the battery grip is overkill unless you are shooting sports all day. It kinda ruins the ergonomics of a light mirrorless body. Just grab a simple ULBTER Tempered Glass Screen Protector for a few bucks and you are good to go.