Here's one for kitchen cabinet painters. We used to do this on the Robinson & Cornish kitchens, so I've got a big bag of them left over. You may use it already, but I think it makes a nice finishing touch.
Here's the problem:
Even though the screw for attaching the knob has been countersunk, it looks less than good.
Here's the solution:
It's called a furniture glide, and is designed to be hammered onto the bottom of wooden furniture legs so they slide over carpets etc.
Knock it in with a nylon hammer.....
And voila. It goes in easily to Tulipwood etc. and will go into MDF with a bit more force. If the knob comes loose, it can be gently prised off and replaced