a certain amount depends on if you are delivering the FINAL trailer,
or of you are just cutting it, offline, then having it re-conformed.
my guess, you are creating the final.
i’d ask for a Prores 422 or ProresHQ of the final graded film,
1920×1080
if the film has substantial use of graphics, or subtitles, ask for a textless version.
as everybody else mentions, you need stems of dialogue, effects, & music.
for web delivery, stereo would be ok
you can also ask for the un-dipped music, or the original music files if that doesn’t exist.
this means that if you want to use some music that has been dipped under dialogue or whatever, you wont be fighting that.
nick