For use with my inventory sheets. Not to be confused with size categories of creatures.

Some items have a limited number of times you can use it, like a quiver with 20 arrows, a bundle of five torches, or a tube of salve with 20 applications. Just keep track of that with a number on the same line.

Pouches and sacks are inherently soft&flexible and you don't have to worry about slots & lines, you can use any sticky note or extra page and can toss all kinds of things in there as long as you don't exceed the counts in tiny items. (In pouches and sacks only: 1 small item: 50 tiny items; 1 medium item: 250 tiny items; 1 big item: 450 tiny items)

This flexibility comes at a cost:

Getting something from a pouch or sack of mixed things costs 1 action; but you can get something from a pouch or sack full of only one kind of thing (for example, a sack of only silver pieces, or a pouch of only slingshot bullets), with your free item interaction. You also don't have to worry about this for spell components.

Retrieving spell components do not cost an action. It doesn't matter where you've stored them.

The special "no-cost" components that a "component pouch" stores take up the equivalent of 50 tiny item slots in a pouch. So it can be a good idea to use a dedicated component pouch for these things.

Components that have a GP cost and/or are consumed are stored like any other items.

My house rule is that Light, Dancing Lights, Produce Flame and Goodberry have costed, consumable components. If you use this house rule:

The components for Light or Produce Flame use a small item for six uses (costs 1 silver).

The components for Goodberry use a small item for one use (costs 5 silver).

The components for Dancing Lights is a tiny item and costs two copper pieces.

All slots can always hold smaller items than the listed size. For example putting a small item, or even a tiny item, in a medium slot.

Five small slots can become a medium slot;
Ten small slots can become a big slot.

A small slot can also hold 1 tiny item. (Which isn't great. So get a pouch…)

You can sew a pouch into the middle part of the flap now, and use it as 250 tiny items.