The most common and most likely answer to this crossword clue is the 11 letter word PAPERWEIGHT
I've seen this crossword clue in The Guardian
P
A
P
E
R
W
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G
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T
More clues leading to the result PAPERWEIGHT
Buddy explains!

The straight part
We know that "that tops the pile" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case that tops the pile = paperweight.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PAPERWEIGHT mean?
PAPERWEIGHT noun- A small, decorative, somewhat weighty object placed on one or more pieces of paper to keep them from fluttering away.
- Any object used for this purpose.
- A useless piece of equipment.