What are the differences between Organic rank results and Snack Pack/Videos rank?

The only difference is that in a Snack Pack/Videos rank, there will be also a letter displayed (for example, the letter C) next to the number (the organic position of the box, for example, #3).

The letter represents the rank of the URL/business/video listing within the element/box.

Displayed as usual, is the number, corresponding to where the element itself (or the box) is ranking (if #3, for example, there are two organic results before it).

In sorting/filtering, the Search Element position rank (#3) behaves just like a regular organic rank.