I've got about 500 rows of data with about a dozen columns. There are
about 100 "items" in the column "A", repeated several times each (hence
the 500 rows), with different rows of data each time

I want to be able to sum up each column for each entry in A

I've already used advanced filter - copy list - unique records only,
so I've set up a unique list of "items", I just want to now be able to
say "look through the 500 rows, every time you find THIS item name, sum
THIS column)

So I will end up with a unique list of items, and a sum total of the
values in each column for that item only

I couldn't remember how to use SUMIF properly, or maybe it needs an
array formula or that clever one SUMPRODUCT?