The only things worth worrying over right now would be a good charger with removable cable. A good cable or 2, perhaps in different lengths. 1TB Micro SD card. Case to keep it clean and safe. A portable power bank which can deliver the required 45W output. Aside from that you may want to consider a kickstand if you intend to use it in a way that is conducive with such an accessory. I have a few recommendations if you'd like to browse the deals I've found

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SD Card -Lexar Play 1TB card, $136 on amazon right now. Appears to be their cheapest 1TB A2 offering from a legitimate company https://smile.amazon.com/Lexar-Compatible-Nintendo-Switch-Smartphones-LMSPLAY001T-BNNNU/dp/B08T8LL7G8/ref=sr_1_3?crid=1CZFNUUGV2ABL&keywords=1tb+micro+sd+card&qid=1657492814&sprefix=%2Caps%2C116&sr=8-3

Case - there are quite a few options already so take your pick but I couldnt stand the over the top appearance of most so I got one of those cheap clear plastic ones for $8 off amazon to hopefully last at least until the Killswitch gets launched

Kickstand - ESR kickstand has been tested and confirmed functional by other users here and its fairly affordable at $11 from Amazon. Part of the reason to have a case is so you dont have to worry about sticking stuff like this or NVME expansions to the Deck directly. https://smile.amazon.com/gp/product/B08FB5GWZZ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Power Bank - This power bank from apoapo is only $30 after coupon code and I have confirmed it will output the necessary wattage to charge a Deck https://smile.amazon.com/gp/product/B09MF1RM9X/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Charger - I have a few recommendations here. This is a go-to option in my opinion. It gives plenty of power but also allows you to charge up to 2 other devices simultaneously. Downside is that it is a bit bulkier. For $26 right now it is the best deal I found so far https://smile.amazon.com/Charger-TECKNET-Foldable-Adapter-Compatible/dp/B08YJLMQGD/ref=sr\_1\_8?crid=274IWDDBDA00M&keywords=gan+charger+45w&qid=1657496234&sprefix=gan+charger+45w%2Caps%2C250&sr=8-8 This option is much smaller but only charges 1 device despite costing $14 more https://smile.amazon.com/Charger-Anker-Adapter-Supported-Foldable/dp/B08T5QVTKW/ref=sr_1_1?crid=1NPL8CRCVQSW2&keywords=gan+charger+45w&qid=1657492960&sprefix=gan+charger+45w%2Caps%2C125&sr=8-1 This Baseus option is for you if you're really trying to get as much utility out of the fewest devices possible, it combines the charger with the power bank with either 2 USB C ports or 1 type C and 1 type A port. The downside is it only charges at 30W from the battery but it will provide 45W from the wall. Also it appears to only be available in white on amazon but there are other retailers that still have the black models in stock https://smile.amazon.com/gp/product/B08D9M1Q6C/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

As far as cords go I'd get ones rated for 100W just in case. Some manufacturers love to over rate their products and you may legitimately need 100W USB C cords now or in the future. You can also get them with a display built in which shows how many watts are being pulled through the cord.

I know the read speeds are higher than what the switch can do but I have this Also have one for my Steam Deck