There are several issues here. First there is retention of shop materials required by the MSCs and second there is retention of materials for IRS. Different MSCs have different retention requirements, with some wanting only until you are paid and others wanting two years etc. For IRS you need to retain materials as long as your return is subject to audit and in the case of businesses, records such as financial records (spreadsheets) need to be kept permanently.
I scan receipts for every shop and these constitute a permanent file for me. I find it convenient to put shop receipts and collateral into a file folder by month. Several months of folders can be put together in a large envelope that is labeled as to the months included. The envelope can be put into a banker's box or other large cardboard box to be out of the way. If I need to find materials from a particular shop, I can pull the envelope to get to the folder for that month and to the needed materials easily enough (which is almost never needed). My box is full so every time I add a new envelope it is time to remove and dump the oldest envelope. This means I am always keeping about the most recent 5 years, which should keep all potential parties satisfied.
Life is too short to try to remember which MSC requires what retention and too short to sort through all old papers to dispose of documents as soon as possible for the MSC.