What does a time traveler eat?

Answer: Pastrami

This pun might be after its 'best by' date.

Explanation for the kids (and bad puns)

Pastrami is a smoked and salted meat, often served as a sandwich on rye bread. Not only does the word begin with 'past' which could be the target of someone traveling back in time, but the name is also derived from an ancient practice of drying and preserving beef. Sounds like a tasty time all around.