My nomination for this thread would multitools. Okay, they're a good way of making sure you've got a variety of tools with you, but they never work as well as individual tools. They're also a good way of making sure you've got tools you'll never need. So perhaps it's not quite accurate to say they'll "never be much use" but they'll certainly not be as useful as specific individual tools. IME.
I feel the same but perhaps more strongly about sporks, which I know have already been mentioned. That said, I do carry a lightweight plastic one with me sometimes as it's great for eating yogurt, which I find to be a good energy-ish pick me up. But for eating anything solid, let alone a real meal, again I'd go for individual "tools".*
And rucksack covers were mentioned too. I tend to see any sort of luggage with a separate waterproof cover as an admission of failure. "We know this needs to be waterproof but we couldn't make it keep the rain out, so here's a fluorescent yellow shower-cap instead."
Not sure about Paramo though. Mine's only rated showerproof, or something similar, but I've found it pretty good at keeping rain out.
*Edit: So why a spork not a plain spoon? Well, it weighs virtually nothing, is easy to clean and... Millets were selling them for beans (something like 25p each). Back when Millets was a thing.
**2nd edit: I realised today that my spork is not exactly a spork. One end is fully spoon, while the other end (which I never use) is a combination of knife and fork: fife? knork?