There is no item, currency, or buff named "Abundance" that you carry in World of Warcraft: Midnight. The phrase mixes two separate things: WoW's "You cannot carry any more of those items" error, which fires when you hit a unique-item cap, and Abundance, the Restoration Druid talent that builds stacks from your active Rejuvenations. Neither one is a bag item you collect.

The two things this query is really about

What you sawWhat it actually isWhat to do
"You cannot carry any more of those items"Unique-item limit. The item's tooltip says Unique or Unique (5) — you already hold the max, counting bags AND bank in some cases.Consume, sell, or destroy one, then loot again. The extra copy stays in the loot window or gets mailed back.
Abundance stacks not going upRestoration Druid talent. It counts your currently active Rejuvenations, not something you accumulate.Let Rejuvenation stay up on more targets. Stacks fall off the moment the HoTs do.
Bags say full but you have slotsReagent bag, profession bag, or a specialty bag that only accepts certain item types.Move the item manually into a general bag slot.

Why does WoW say I can't carry more of an item?

Almost always a unique flag. Blizzard caps quest items, event tokens, keys, seasonal currencies-as-items and some crafting reagents so you can't stockpile them. Hover the item and read the line under its name: "Unique" means one, "Unique (3)" means three total. Bank contents count toward the cap on unique-equipped and many quest items, so a forgotten copy in the bank is the usual culprit.

The second-most common cause is a soft cap you didn't notice — a weekly cache, a quest that only wants five of something, or an item that stops dropping once you own the maximum.

What is the Abundance talent in Restoration Druid?

Abundance is a passive that watches how many Rejuvenations you have rolling. Each active one reduces the cost of Regrowth and pushes its crit chance up. It's a throughput lever for heavy-blanket Resto play, not a resource you bank between pulls.

If your stacks look wrong, it's a HoT-uptime problem. Track your Rejuvenation count on your frames and you'll see the number move in real time.

Is "Abundance" a Midnight zone, item or system?

No. Midnight brings Quel'Thalas, housing, and a new season structure, but nothing named Abundance ships as a collectible or currency. If a guide or video told you otherwise, check the source — mis-transcribed talent names and outright made-up items circulate fast around expansion launches. Blizzard's own tooltip and the in-game Adventure Guide are the only things worth trusting on a name.

How do I stop bag-full errors during a raid or key?

Clear before you pull. Vendor greys, mail crafting mats to an alt, and keep at least six free slots before a Mythic+ key or a raid night. Unique-item errors specifically won't be solved by free space — you need to get rid of the duplicate you're already holding.

If you'd rather spend your evenings clearing content than untangling tooltips, PewPewShop's vetted human players do Mythic+ keys, raid progression and rated PvP as play-together sessions and one-on-one coaching. A Resto Druid coach will fix your Rejuvenation uptime in a single session — usually a fraction of the cost of a full carry, and you keep the improvement. No bots, no cheats, long clean record.