I can't believe I didn't see a thread like this already. Is there already a function where players can deal with their entire inventory at once? I'm getting sick of deleting 40 useless items one by one!

Yup. It's called QuickStock, and you can find it in your shop options. It allows to you stick items in your Vault, Shop, Wardobe, Donate, or Keep.

Yep, instead of destroying, you could always donate it.

One man's trash is another mans treasure.