These soft and squishy silicon earplugs are my go-to for travelling. They are reusable several times (I usually wear mine a few weeks before they lose their 'stickiness'). I warm them up in my hands then make a little point to poke a little way into my ear canal. The effect is silence! Airplanes, hotel air conditioners, snoring partners...
They come in sets of three in a little plastic case.