Getting a good (well, at least passable) night’s sleep can be a big factor in your climbing success. A tent flapping in the wind or a snoring tentmate can be easily thwarted with the humble earplug.
Tip – buy a pair that’s connected with a foot or so of string. When one falls out (and it will) it can be easily retrieved and won’t be engulfed to the folds of your sleeping bag.
Carry them in a film can (remember those, digital camera users?) or other small plastic vial so the string does not get tangled up. Get the plugs a good hardware store. They do get lost, even with the string, so get 2-3 pair when you’re shopping.