We do something like this:

Financial:
Invoices are filed sequentially by invoice number.
Bills from regular suppliers on account are filed by supplier.
Bills from occasional suppliers on account are filed in a single file sequentially by date.
Bills for capital purchases are kept in a file with all other paperwork on that asset.
Bills paid COD are filed sequentially by date. Each "method of payment" has its own file.
Bank statements are filed sequentially by account. That file is in three sections: Bank statements, cheques and notices from the bank.

In the days when everything was paid by cheque, the cheque would be attached to the paid bill. But with internet banking those days are long gone. We probably write less than 100 cheques a year!

This system relies on accurate capture in the computerised accounting program to quickly be able to lay hands on any given document. And it works quite well.

I'll set out how we deal with non-financial document filing tomorrow.