"Clear" out sounds better to me than "clean" out.  When did
you last clean out your swim bag?  Having clear space just feels good.
NOW is the perfect time to clear out backpacks, fin bags, book bags,
swim bags, water bottles, snack areas, pantries, drawers, closets,
mudrooms, etc.  Start with one item or area only; maybe SWIM BAG
for starters.

Try this simple system below:

CLEAR OUT.  Take out everything.  
Sort items into 3 piles: keep, throw away, put back where it belongs.

WIPE DOWN.  Run it through the wash if needed.  
Usually warm water with soap and a tiny bit of bleach 
will do the trick for mildew.  (or is that only something 
that happens at my house?)

RELOAD. Replace items back where they belong.  
Group similar items.  Keep only what is needed so you don't waste 
valuable time searching for what you need.