A lot of drummers these days work with various artists, musicians and bands along with having their full-time band/project. This is possible only if you are a good musician (irrespective of the instrument you play), able to gel with other musicians coming from various backgrounds, have the ability to play to a click track, work out different songs with less efforts, etc. The most important factor of working as a session drummer is to know your gear and setup.
It is not required for you to play on a huge setup, variety of grooves, extraordinary fills. It is more important to understand what would best do justice to a song you are working or playing to. Knowing the right set of gear like the size of the toms, bass drums and snare, the drum heads for each of them and set of cymbals that would best suit the setup and the song. There are various options available from Mapex/Pearl and a range of drumheads from Evans which will never disappoint you!
Your gear should not just be the correct one, but it is extremely important that it is well maintained, so the best sound from it can be achieved.
Playing to click track is extremely important if you want to be a successful session musician. Try working your parts out with lower BPM (Beats Per Minute) on the device and then finally play it to the actual tempo of the song. That really helps to work on each hit and plan the movements and grooves better.