spare snare (I alays had one in reserve in case I blew a head live) and maybe some other snares. But these days, they can make a text book sound good with all the crap available to the engineers.

I will reiterate that all gear should be in top form- new (or recently changed) heads, all bearings/moving points lubricated. Do this the day/night before; not the morning of! Any "iffy" nuts, bolts etc. should be tended too. All cymbal stands should have some vinyl tubing on the center bolt to avoid squeaks (and reduce "keyholing"). Spare snare heads (top and bottom), sticks and maybe a change of clothes if you get sweaty easily. Comfortable shoes too!

Bring moon gel and zero rings (whatever you prefer). You may need to control a drum in that room that normally is fine wide open. You can have "reverb" added in the mix later if desired. Make sure the drums sound the way you want them to.

Also be well rested, and well-fed (not over-fed) the morning of. Have plenty of water available and maybe snacks such as peanuts or granola bars with high protein content. Avoid "junk" like chips etc. Try not to choose messy foods. (You may not be allowed to bring any food or drink in the studio). Chances are you will be having a late lunch, or no lunch!