A well-equipped party should always be ready to make its mark.
"Kilroy was here" was a piece of graffiti painted around the world during World War II. The origin of Kilroy is debated. What is not debatable is Kilroy went everywhere. Years ago, a character in my campaign walked up to a wall and wrote, "Julian was here". That started my interest in having my dungeons show that someone was here before.
Chalk is lightweight and common. Some of the earliest cave drawing are drawn in chalk. Throughout history, chalk has marked walls with graffiti. Chalk provides an easy way for a character to leave their mark on the dungeon, for example, "Julian kilt an ogre here". Which is a pun on the carving in Washington County, Tennessee which reads, "D. Book Cilled a. Bar on tree in the year 1760".
Chalk is invaluable if you wander into a maze. Chalk allows you to quickly and easily mark the path you took. This makes is much harder to get lost. The disadvantage is this allows other things to follow you.
Weightlifters, gymnasts, and rock climbers chalk their hands. Athletes competing in power field events, such as shot put, discus throw, and javelin throw, use chalk to aid in gripping.
Putting chalk powder on the floor is an easy way to see if anything passed that way, or to reveal an invisible creatures foot prints.