Shortly after I started swimming often, my cap ripped one morning as I put it on my head. I was in a Masters group at the time and fortunately another swimmer had an extra that she kindly lent me.
Ever since that day I have carried an extra cap around in my swim bag.
Earlier this week my goggle strap snapped right in half. Fortunately I happened to have an extra pair so it was a quick walk to the locker room instead of a missed swim or a cold trip to the car to get money to pay for a new pair from the pool.
Caps and goggles are two little items, but ones that break from time to time with constant use. I highly recommend just throwing spares into your bag so that when they break it will not ruin your swim.