The waste occurred when the item was manufactured, not when it was sent to you. Given that nobody wants it, creating it was a destruction of the value of the raw materials that went into it. Whether you throw it away or do anything else with it is irrelevant; the value is already destroyed.

Worrying about the fate of that watch-strap is a bit like fishing some food-soaked plastic wrap out of your garbage bin, and then feeling bad about throwing it back into the garbage bin. The plastic became non-recyclable earlier on, when it interacted with the food during packaging. It interacted with the food before you ever bought it. The standalone recovery-value of the plastic wrap was destroyed in the manufacturing facility, and would be destroyed whether or not you chose to buy the item. Just like those cheap watch straps nobody wants would have been manufactured whether or not there was demand for them. (Because there isn't demand for them, and they still clearly are manufactured.)