Here is how I have redundancy.A multi tool or SAK is a back up to my 3 inch locking folder.The folder is a back up to my fixed blade sheath knife when carried.They are all used interchangably depending on the task at hand.
Some things can be back ups with out repeating.Water filters can be backed up by purification tablets.If your water bottle is a Guyot or Klean Kanteen you can boil your water in it.
The main idea is a back up for critical items that are hard or impossible to recreate in the wild is strongly recommended.

BOATMAN
John