Only races I’ve done I’ve not bothered with spares. They’ve only been around an hour long and I know that by the time I change a tube, or attempt to fix something else (I’m not particularly mechanically minded) my race will be over anyway!
That said, that’s always been on a course where in that hour you can do around 4 laps so although it’d be a pain it’s going to be a particularly long walk back. Touch wood not had any mechanicals yet, and only 1 crash (yes…the hole in the arm one!), and that was thankfully near the start (and therefore the “road”!)
I wouldn’t carry any more than tube, levers, co2, a powerlink and a small multitool.