Synonyms for Straight off:

adv.

directly (adverb)
instant, now, right away, immediately, instantly, forthwith, first off, right off, straightaway, at once.

n.

straight off (noun)
forthwith, at once, in real time, right away, instantly, directly, now, immediately, straightaway.
without delay (noun)
first off, instant, time, right off.

Other synonyms:

without delay
instant, right off.
Other relevant words:
right off, instant, first off.