| We have had many lengthy and highly informative threads at TalkBass which answer your very questions. If you do a search you will find some of those discussions.
If you will be doing some blues gigs, ask the group what their set list usually is and have them tell you the names of songs they commonly play. The list of commonly played blues songs is quite lengthy, but luckily for you, we have run many such lists here at TalkBass also...everything from "Stormy Monday" to "The Thrill Is Gone."
What you might be playing may depend on the style of blues your band plays, traditional Mississippi blues, Chicago blues, blues-rock, Texas swing, St Louis, originals or covers, whatever. Also, know the difference between a minor and major blues.
As for scales, you absolutely must be familiar with the blues scale. You should also know the mixolydian scale, minor pentatonic scale and, of course, the major scale.
You should also know the most common blues grooves, such as the all important 12/8 shuffle, but also the straight eighth feel, quarter-note feel and eighth- note feel, and know how to "walk."
You say you know the I, IV, V thing, (I assume you also mean the 12-bar blues progression) but do you know about turnarounds, and can you play credible intros, fills and exits? By credible, I mean something that is appropriate for the style and groove of blues your band is playing.
Blues gigs are great fun. Personally I love blues music and I hope you will develop an equal affinity for the blues. Meantime, do a TalkBass search so that you can find much more complete answers to your questions.
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"Jazz sounds like a very good blues band that fell down a flight of stairs."
Michael Buble, Canadian standards singer | 
