bring a bike tube, and when you bring a bike tube, make sure that it fits
but if not, a 700c tube will fit in a 650b tire.
bring an extra tube
take off your gloves so you can feel the tire and find the tiny piece of wood that popped the tube
pump your tires to the correct pressure. when in doubt, go higher. it is easier to let air out on a break, than to pump it up.
a small, quality frame pump is worth it. it is good that you bought the metal one.
a mountain bike is slower than a gravel bike, but you can still do events on a mountain bike, it is just slower than a gravel bike. 😛
cue sheets should cut down to cue cards and they should be strapped onto your handlebar with a holder. or get a bike computer that does GPS directions, but they cost a few hundred dollars. or get one used. or ride with people that have them. or ask for directions. or figure out how to get your phone to give you directions.
brings lots of food. more than you think. you may eat it all. i did.
clear safety glasses were important
a wool short sleeve tshirt plus arm warmers is a magical combination. putting a cycling jersey on top could be even better.
rain can completely change the course. like the mountain bike would be good on that course.
you dn not need a front shock.
a cycling cap is nice to keep dust and dirt off. if it is complete mud pit, then go with a longer cap.
cycling shorts save your ass. or taint. and various other bits down there.
they are a lot of fun, especially if you have a group that is willing to put up with you.