Whether a Player Character has Salt on their Person if it is not specifically listed as gear on their sheet is Up To The GM.
Some GMs require that anything you have be explicitly listed on your inventory (which can lead to some very long inventories listed on separate pieces of paper at times). Including like, twine, or a sewing needle, or a tin fork. Other GMs allow characters to have items that it would make sense for that character to have, and that aren't especially valuable or heavy. Some other GMs will roll for whether or not a character has an item, whether a pure luck roll or something based on a skill or ability check.
DnD 5e has no explicit rules that I know of that enforce any of this in any way. Even if they did, the GM could houserule that (and may without even knowing such a rule exists, as I don't).
The only real limiting factor on the GM here is what the table considers reasonable. If you for example start saying that the rogue can't place a thread over a doorjamb because a 'Traveling Outfit' doesn't explicitly say it's made out of cloth rather than say, purely leather (ugh), many players will find that dissatisfying or unverisimilitudinous and may become less interested in the game as a result.
As for the different but related question is it reasonable for a dnd character to have some salt for cooking on their person? i'd say it could go either way. Most travellers in historical times would start fires and cook food even if it was dried or salted or otherwise preserved, as cooked food is tastier than preserved food generally, especially given the specific ingredients available at the time. Living on 'dry rations' alone was considered to be bad or even torturous, and there are countless tales of soldiers cooking or brewing tea in their helmets for lack of pots, techniques that have survived to the modern day for cooking with almost no utensils over an open flame (spit roasting, 'rock pots' with heated stones, cooking inside animal skin bags), and so on.
So there's every reason for a medieval or dnd character to have some salt about their person, from cooking to its efficacy in dealing with parasites or wounds. But whether some specific adventurer does or not is largely up to the GM.
My advice in general though would be that GMs should have a consistent policy on inventory vs 'assumed' goods, and that players should endeavour to discover this (amongst the various other common GM differences and 'table rules' that change from group to group) so as to create a believable narrative for their character (which mostly just means writing down a big list of items or.. not needing to, in this case).