Being able to recognise by ear, intervals, chord progressions and the "quality" of a chord (minor/major/dom7/etc) has been the single most useful thing for me when being asked to play with others, particularly for the first time.
I read, but have only been asked to read dots once in 35 years. I'm afraid to say as I hate musicals, I tend not to go for pit work, as I'm likely to walk out the moment someone starts to sing what they should just @**#$ say.
All the Jazz stuff I do is with chord charts, as I tend only to play standards, and not the more grown up high brow stuff.
I think Doddy is right, reading gives you more options. If you can't read then being able to hear and recognise what is being played can be quite handy too.