Bandage

well... just calling to ask.
did you ever take off that gross bandage...?

Sans, if the Bandage has never been removed during a Neutral Route

The Bandage (JP: ほうたい) is the armor equipped to the protagonist at the beginning of Undertale. Its offensive counterpart is the Stick.

Additional uses

After unequipping the Bandage, it becomes a healing item, healing 10 HP.
If the Bandage is equipped, it almost always (exceptions being most boss fights and Hard Mode) grants the protagonist a 100% chance of successfully fleeing from battles.

According to Legends of Localization Book 3: UNDERTALE, the ambiguity of the item's English name is intentional; it is meant to be unclear to the player whether the bandage is meant to be like a band-aid or more like a strip of cloth. As Japanese uses two different words for these concepts, the localization was forced to make a choice, opting for the latter.^[1]

↑ "The main character starts with the “Bandage” item. In English, “bandage” can refer to either an adhesive bandage or a bandage wrap. This ambiguity was intentional, but late-game text suggests “bandage wrap” was intended.

In Japanese, however, these two types of bandages go by different names: bansōkō (“adhesive bandage”) and hōtai (“bandage wrap”). Unfortunately, this language difference forced the translator to use hōtai, which removes the intended ambiguity and prevents Japanese players from experiencing the same confusion as English-speaking players." — Clyde Mandelin, Legends of Localization Book 3: UNDERTALE, pg. 87