If you need to sharpen up a small blade or metal tool, a few swipes on an emery boad will do in a pinch. Sometimes the simplest hacks are also the most effective.
If you find yourself needing to sharpen up a small blade like an X-acto knife or tools like tweezers, follow the suggestion from One Good Thing by Jillee and pull the item a few times in the same direction across an emery board. Obviously, you'd get better results with a sharpening stone (or a fresh tool), but if you just don't have them around, this works pretty well. Emery boards are also great for shaping up the point on pencils.
12 Handy Uses for Emery Boards [One Good Thing by Jillee]