From your comment here, I now understand that "se" is a suffix appended to some form of the verb, and that it can be broken off and used elsewhere in a statement or sentence, the position of "se" can be transposed, it is fluid. I understand the reflexive quality of "se" and the importance of the nuances that drive its use. In one discussion somebody said "so we throw se in there", now I understand this. Thanks.
I have to agree with joarvat. "Se comieron once emparedados" could mean "Eleven sandwiches were eaten," with se comieron as the passive past tense plural conjugation of comer.
Comerse can also mean "eat up" instead of just "eat" (for more emphasis, as some people have already posted).
In my mind, the two most correct translations are "Eleven sandwiches were eaten" and "They ate up eleven sandwiches."