In the Scholar's pack on page 151 of the PHB it notes that you get a 'little bag of sand'. Is there any mention of what the intended use of that is in-game? I haven't found anything in the equipment chapter.
Given the volume of off-topic answers I'll summarize the question as so: Why is it given to Scholars specifically; what use is the bag of sand to a scribe or other scholarly person?
Sand is one thing used by scribes to blot ink, so that a document can be handled or moved soon after working on it, without dripping or smearing. You can assume it sees use as a matter of course while the character is mapping a dungeon or composing a letter.
Apart from that intended use in a scholar's pack, it can probably be put to many creative uses under dire circumstances that have nothing to do with ancient ink's inconveniently-long drying time.
The classic, cinematic use of a bag of sand by a scholar comes from the opening scene of Raiders of the Lost Ark in which it is used in an attempt to disable a weight-sensitive trap. Shame Harrison fluffed his roll.
That said, D&D 5 harkens back to the era of having players find creative solutions to problems (as opposed to rolling dice to let the characters find them which become more common from 3.x), so it probably doesn't have any specific intended use. It is there to spark creativity.
Use it to mark a trail, hit a goblin (if you can't find a half brick), draw mystic symbols, make a Mind Flayer's undergarments uncomfortable to wear, reveal an invisible bridge (Indy really did like his sand), or whatever else you can come up with.
Arguably, it could work as a material component for the spell "Sleep" since one of the options are "A pinch of fine sand."
I think that the intended purpose is to use your imagination. The bag of sand is just like the various trinkets you get, they don't have something built into the system for their use.
Here are a few possibilities for a bag of sand:
You can use it to exfoliate before going to a ball where you intend to assassinate a corrupt local merchant.
You can use it to remove the rust from a corroded metal plaque to read the symbols underneath.
Use it to test the direction of the wind.
Sprinkle it on the floor so that an invisible creature leaves footprints.
For a charismatic character with the charlatan background, sell it as fairy dust.
