There are different sizes for various items to be considered significant in regard to carrying. If one carries an insignificant item, they are exempt from a Korban. For example, all human foods are significant if they are the size of a dried fig, but animal foods have different sizes. (Processed straw the amount to fill mouth of a cow, straw from beans the amount to fill mouth of a camel, unprocessed straw the size to fill mouth of a lamb, grass to fill the moth of a kid, etc)

There are 3 opinions for tho these sizes work. Our tanna holds these sizes are given for ordinary cases, but if someone specifically stores a smaller size for a particular use, it becomes “signficant” to them, and they would be obligated if they subsequently carried it out. R Shimon Ben Elazar is even more stringent and he adds that is Reuven specifically stored a smaller size, even Shimon would be obligated if he carried it out. R Shimon is most lenient and he says even if one stores away a smaller size, they are not obligated if they carry it. (Furthermore, he holds that all the sizes mentioned are only for an average person, but a rich mans items are only significant in larger sizes)

Straw is fed to cows and the size is therefore to fill mouth of a cow. If someone carries out straw with intent to feed it to a camel, they are still obligated even though it won’t fill the camels mouth bc it is still a significant item.

Straw from beans is usually fed to camels and not cows and the size is therefore to fill camels mouth. If someone carried out straw from beans the size of cows mouth with intent to feed a cow, it is a dispute whether that intent makes the item significant or not. The root of the question is that this bean straw will be “forced eating” for the cow and that may not be called eating.

Generally, there is a principle that items in Halacha with different sizes can not combine to make a שיעור. However, if the items are sometimes used together, they can combine for the more lenient amount. To illustrate: straw (to fill cows moth) and straw from beans (to fill camels mouth) have diff sizes. If one carries some regular straw and some straw from beans that together add up to the requisite size of filling a camels mouth, they are obligated. (If they only amount to the size of a cows mouth, he is exempt) The reason they can combine is bc these items are sometimes used together by a shopkeeper to bundle together samples outside the stoor.

All people foods size is like a dried fig. If someone carries flour and it only amounts to a dried fig if the bran is included, they are exempt bc bran is not a food. However, regarding the size for הפרשת חלה we do incorporate the bran in the size bc sometimes poor people bake bread without separating the bran.

R Yehuda holds that shells of lentils are food and part of the amount. Shells of fresh beans as well, but shells of dried beans are not food bc their black appearance makes them look like bugs in the food and no one eats it.

the size for most liquids is רביעית. However, wine is significant with 1/4 of a Reviis, bc it’s made to dilute with 3 parts of water and total a reviis for כוס של ברכה.