These words are essential:
et tu brute
veni vidi vici
Here's some others you can use to fill in:
friends romans countrymen ears
gaius
kai su technon (or texnon if you like)
rubicon
gallia est divisa in partes tres
de bello
octavian
some latin words you can use as fillers:
ut
ego
illa
ille
hic haec hoc
bellum bellum bella
res rem rei rerum
interfecit, occidit, conficit, exanimat (they all mean kill, bloodthirsty lot the romans)
fossa