Split once, paste twelve times
1. Select the list in its source. A spreadsheet column, a block of lines in a doc, a comma-separated string in a ticket.
2. Press ⌃⌥⌘C. Each piece arrives in the Stack as its own item.
3. Choose an after-paste key in the "After:" menu at the bottom of the panel. Tab for a web form, ↓ for a spreadsheet column.
4. Click the first target field and press ⌃⌘V once per item.
Splitting happens on lines, commas and semicolons, which covers most lists people actually copy. Names, SKUs, emails, invoice numbers, tracking codes.
The pieces are ordinary Stack items once they land, so everything else still applies. Drag a row to reorder it, delete a piece you do not need with ⌘⌫, click a row to restart the queue from there.
There is a second route for text you already copied. Open the item's preview in the popup and press the Split button in the footer. The same split runs on it, which is useful when the source window is gone and all you have left is the copy.
The traps
Quoted commas break a comma split. A CSV line like "Smith, John",acme.com has a comma inside the quotes, and the split does not know that comma is part of a name. Split that one by line instead, or clean the field first.
Only three delimiters. Lines, commas and semicolons. A pipe-separated or tab-separated list needs a find-and-replace before you split, so nothing surprising happens.
Check the count before you paste. The Stack shows how many items it holds. If your list had twelve rows and the panel says thirteen, a stray blank line or a trailing comma made an extra item, and every field after that point would be off by one.
Where you do not need this
If the target is a spreadsheet column, plain pasting already works. Copy a block of lines, click a cell, press ⌘V, and Numbers or Excel spreads the lines down the column for free. Text to Columns handles the comma case natively, and it is free too.
Splitting into Stack items earns its place when the targets are not one contiguous range. Separate fields on a web form, twelve invite boxes, one value per app, or a mix of the three. The system clipboard cannot help you there, because it holds one item at a time and every copy destroys the last.
What I use
⌃⌥⌘C, mostly for pasting a list of emails into invite fields one by one. It is part of Klipto Pro, $19.99 once with updates included, and there is a 14-day trial if you want to test it on your own lists first.
For plain clipboard history with no splitting and no queue, Maccy is free, open source and 1.6 MB. I used it for years before I forked it.