https://www.amazon.com/Sleeve-Kings-Card-Sleeves-63-5x88mm/dp/B07RD9QZD2/ref=mp_s_a_1_4?dchild=1&keywords=63.5+x+88&qid=1611609623&sr=8-4 I use these sleeves. They are inexpensive clear sleeves and work very well
My card storage for an All-in pledge for campaign 1. Wanted to keep all the art work, but cut down (pun intended) on all the space the boxes took up. All cards, locations, and villain dashboards fit. I currently just have all the minis unpainted and jumbled in a mess in the stretch goal box until I finalize how I'll fit them all in there. I will also be 3d printing the token holder shared in this group, which should fit in this box with some slight rearranging of the cards. (https://www.etsy.com/shop/JSquaredDesignStudio)
I should also be able to fit the cardboard villain dashboards when I get those with my X-men All-in. My goal is to have all of each campaign in just 2 boxes. My only thing right now is trying to decide what to do with the gauntlet.
Box used: BCW Monster Storage Box, Holds 3,200 Standard Sized Trading Cards, 200 Pound Test Strength (1-Count) https://www.amazon.com/dp/B000K41E6K/ref=cm_sw_r_apan_glt_fabc_BGYCPPQZDEYRGTRTM0KV
Sleeves used: KMC Perfect Size Sleeves Topload Standard Size [10 Packs] USA Packaging https://www.amazon.com/dp/B08KYD29L8/ref=cm_sw_r_apan_glt_fabc_4AN2VKFY71W86BT2EHYB?_encoding=UTF8&psc=1
These were pricier, but I really like them. I will be using different ones for the second campaign to save some money
Sleeve Kings Card Game Card Sleeves (63.5x88mm) - 110 Pack, 60 Microns https://www.amazon.com/dp/B07RD9QZD2/ref=cm_sw_r_apan_glt_fabc_76YBGQ4N39NPSRAY15FK?_encoding=UTF8&psc=1
Dividers used: https://boardgamegeek.com/filepage/220250/horizontal-card-dividers
I taped a piece of index card to them to raise them above the cards, since they are actually the same height as the cards.
EDIT- Hiding links isnt working on mobile so I'm just gonna display the link underneath.
If you're looking for upgrades that are specifically made for Marvel Champions, that stuff is usually on etsy or a dedicated site like burger tokens.
If you're looking for generic upgrades that can be used on marvel champions, there's a ton of options.
Sleeve Kings are an affordable brand of sleeves that still provide quality. I use them for my whole collection.
Link-Sleeve Kings Card Game Card Sleeves (63.5x88mm) - 110 Pack, 60 Microns https://www.amazon.com/dp/B07RD9QZD2/ref=cm_sw_r_apan_glt_i_H3RMF9AW35J7H4BKP2B0
There are plenty of playmats for sale too. None of them are the official marvel champions ones but they provide the exact same function. I personally bought 2 of the generic double pack because it's way cheaper, and essentially gave me four times as much coverage for other games too.
Link-Black Card Game Mats, TCG Playmat (24 x 14 in, 2 Pack) https://www.amazon.com/dp/B08YR92T5R/ref=cm_sw_r_apan_glt_i_BZ7KMCYSNFPNB4MPQKS9
Finally there's tons of cardholders if you're interested in those too. I bought this set of 4 but tbh i don't love it because it obscures the resources in the corner and i just prefer holding cards in my hand.
Link- Exqline Wood Curved Playing Card Holder Racks Tray Set of 4 for Kids Seniors Adults - 13.4inch with Widen Base Stable Enough for for Bridge Canasta Foot and Hand https://www.amazon.com/dp/B086PJFW2Y/ref=cm_sw_r_apan_glt_i_0WP2BTBD9NWBVCT7TVPS?_encoding=UTF8&psc=1
https://www.amazon.com/Sleeve-Kings-Card-Sleeves-63-5x88mm/dp/B07RD9QZD2
this is the standard size.
i use these and i like them. they are a bit slippy so they are good for mash shuffling but big stacks will fall over easily.
there are many other sleeves with pros and cons. its hard to say which is really the best.