It doesn't have to be "all or none." I keep the complete file of backup for each return for three years from the due date. At that time, I skinny each file down to the very basics (W2s, 1099s, hard copy of full signed return, DAF contribution acknowledgement, spreadsheet printout showing calculations). The hanging file is deactivated and the entire remainder is placed into a clearly labeled manila envelope with clasp flap. The label on the envelope indicates that it can be disposed of at time of estate closure. All other support is disposed of at that time.
I am not a lawyer, accountant or financial advisor. Any advice or suggestions that I may provide shall be considered for entertainment purposes only.