First on everyones list of activities should be public transportation, the STM is running the Metro all night, also there are free shuttle buses which travel through primary locations of the festival.
With 200 activities in a span of 12 hours, you don’t want to waste time looking for parking or in traffic. If you plan on making several trips, the Unlimited Evening pass is wise option. The pass costs $5.25 and is valid for unlimited travel between 6 p.m. and 5 a.m. the next morning.
More information: Société de transport de Montréal (STM)