However, Paypal didn't go through. I almost never use paypal, and suddenly $4k+ purchase so it triggered fraud alert and didn't let me complete the deal. Called them few times to fix, but they were not really reassuring to fix it so put it on my cc instead.
What else should I buy now? One extra battery for sure. The charger is already double charger, so that's good. What else?
(Trying not to jump and down here with excitement)
Fast CF cards if you don't have them. If you use an Arca-compatible tripod set up, the RRS L bracket is a thing of beauty...it's modular, I leave the upright portion off if I'm not bringing a tripod with me.
If you use one of Canon's little IR remotes (RC-#), unfortunately those do not work with 1-series bodies, so you may want to look into a radio trigger solution (I use the hähnel trigger as the transmitter is reasonably small).
I got the fast Lexars already (2 of them), which actually leads me to a question: is there certain way I should use those? Does it automatically continue with second card after first is full (I assume yes), anything else there?
I have cheap-ish tripod, so not Arca.
Is the trigger port same as 5D3? I already have wired intervalometer, plus cheap Chinese wireless trigger (the receiver is wired to the port). If the port is same, I'll keep using those.
A second battery as you mentioned can be a good idea, but to be honest it is amazing how long just one lasts for if you are shooting stills (even sports). It is video which drains the battery quite quick. They are pricey, but at least having a full spare handy can be reassuring. I have a second and have used it, especially when shooting a mixture of stills and video. With just shooting stills, one battery really does last an amazing amount of time - incredible technology.
As for your question about the CF cards, yes once the first card is full it automatically switches to the second card. This may depend on your settings, but that is how it works for me. I work with RAW only and it writes to just one card (under my settings). I have two 64GB Lexar 1066X in my 1D X and it is quite hard to fill them both. There are quite a few different settings you could choose as in what is written to where etc.