I am doing it using spreadsheet (I prepared it 10..15 years ago and I I don’t feel the need to change it).
At one tab I have a list of all elements I use. Having columns with symbol and footprint and then next column with description of part (really I have 2 columns as since RoHS was introduced I decided to have in the same output the info where I have RoHS declaration for each part). For some parts I have in one cell a list of accepted by me parts to be used (like 1G gates coming from several manufacturers).
In past (with Protel) I used assumption: one symbol = one part so I had 1k symbol for 1k 0603 and 1k_4 symbol for 1k 0402. When I moved to KiCad (2017) I changed my assumption to symbol+footprint = one part so I can have at schematic two resistors having 1k symbol and one is 0603 and the other 0402.
I load csv received from KiCad schematic (not PCB) into tab 2 of my spreadsheet and I have there equations concatenating symbol + footprint and finding at tab 1 the row having the same symbol+footprint and filling the rest fields with right data from first tab.
To tell you the truth I practically copy tab2 into next tab (name it with PCB name) and do everything
there. So now I have in this spreadsheet about 10 BOMs of last PCBs I have designed. Once per several years I’m tidying up and throwing away old tabs.
The bom (having equations in them) I copy and in another spreadsheet I paste it in only text mode to have bom being not dependent on first tab. After getting csv it takes minute to get the output BOM provided all elements are in first tab. Frequently on this stage I have to complement the first tab with new elements I have used in new PCB so it takes some more time.
Some time ago after such descrition I was asked to show my spreadsheet so I have done it:
But since V8 I have changed my work a little as from current BOM generated csv I don’t have to select a part of it but after opening it as text I can select the whole file using Ctrl+A. I have also checked that I can even not generate csv file but can copy data directly from BOM window (I left only needed by me columns and made them in order I want them.