To my understanding, the amount of spice you can take out of Heward's Handy Spice Pouch is theoretically infinite per charge, since I assume they are redefining the word "pinch" in the description to "enough (amount) to season a single meal". Wouldn't that mean I could create enough seasoning to season a world's worth of food? Is my interpretation correct? Obviously it's not balanced, and classical RAI would say I'm only partly correct, but I would personally like to have a finer idea of what's solidly within and without both RAI and RAW bounds, so a simple question like this would help. Anyway, here's the definition, emphasis mine:
This belt pouch appears empty and has 10 charges. While holding the pouch, you can use an action to expend 1 of its charges, speak the name of any nonmagical food seasoning (such as salt, pepper, saffron, or cilantro), and remove a pinch of the desired seasoning from the pouch. A pinch is enough to season a single meal. The pouch regains 1d6 + 4 expended charges daily at dawn.
Depending on the answer I get from this question, I might ask a reasonable homebrew to mitigate the abuse of this, but I'll postpone that for later.
Best Answer
No, the interpretation is not valid. You get normal pinches and can't produce unlimited wealth from a common item
The pouch says (emphasis added):
English words have their common meaning, so a pinch is (Oxford languages):
That is the amount. It is able to season a single meal. When the haversack speaks about seasoning a single meal, that is a single meal, for a single person.
You might argue that a meal for a giant might not reasonably be seasoned by a single pinch, as it is too large, but that still works: this is a magic item and the item says the pinch is sufficient to season the meal. Its magic. And even if you went with your interpretation of a meal for the world (which I think is quite obviously not the intended one), this one small pinch would be all that is needed. You don't get more spice.
Commmon magic items
Consider also this introduction to common magic items in Xanathar's Guide to Everything (p. 136):
Being able to create unlimited amounts of highly valuable spices would be economy breaking and quite powerful. Saffron is a trade good and one pound of it is worth 15 gp, freely useable to trade. Being able to create unlimted amounts of it is equivalent to being able to create arbitrary amounts of gold. This cannot be the purpose of this common magic item. It‘s to have some fun roleplaying that you can cook delicious meals for your party (or some important NPC) because you have this cool, magic spice bag.