Question

Which slogan contains alliteration?

Answer 1

Answer:The Snack You Can Sneak

Explanation:

Answer 2

Alliteration refers to the stylistic device wherein a number of words, which have the same 1st consonant sound, occur closely within a series.

Some obvious examples of alliteration are:
-Alice’s aunt ate apples and acorns around August.
-But a better butter makes a batter better

Among your choices, the closest representation of alliteration is The Snack You Can Sneak. Although the choice "Simply the Best Snacks" does have 2 S's. The former has a better creative and rhythmic value.
 
So I would go for "The Snack You Can Sneak" as the best answer here.