I was able to pick up a Lexar 512Gb with SD adapter card on Amazon for what didn’t seem like too crazy of a price.

I have an Anker PowerCore+ 26800mAh PD which delivers up to 45W PD, which as far as I know should be just as good for juicing the Steam Deck as the actual charger.

https://www.amazon.com/Anker-Charger-PowerCore-Portable-Delivery/dp/B07XRJZXKY

Bit pricey, but well worth it. And the capacity will definitely top it up several times over. The Steam Deck has about a 5300 mAh battery if memory serves; even accounting for some efficiency losses from the power bank to the device, it should still charge the Deck at least four (possibly five) times over before it itself needs recharging. That'll give you a pretty solid amount of portable playtime. Possibly more importantly, it's still considered airplane-safe as part of your carry-on luggage, which can restrict anything over 27,000 mAh.

SD Cards, obviously as big as you're comfortable with. Just make sure they're UHS-1 for maximum speed. Any reputable brand will do, just make sure you get it from a proper seller on Amazon (preferably from Amazon themselves) and not Fleabay, and pay attention to the prices - if it seems too good to be true, and similar ones aren't fairly close to it in price, then it's probably a scam.

This 512 GB one will do for a lot of people and won't break the bank:

https://www.amazon.com/Lexar-High-Performance-512GB-microSDXC-UHS-I/dp/B07KBQQ82D/

Hopefully in a few weeks I'll have my email too. At the rate that they've been pushing that queue, I might have my email in a week (I'd be likely one of the very last ones in that batch assuming they can push about 1h7m or so each of the next few ship dates), or failing that, next Thursday at latest.

Just in time for my birthday. :)