You could bring turbos or rollers, but usually for crits I give it 10-15 minutes gassing it around the back streets. A few high cadence efforts, and some hard sprints up to about 85% max heart rate is usually enough to get ready. The first 2-3 laps will have you plenty warmed up after that.

For something like the Pickering brook races I’ll always take my trainer to keep the legs good during the wait between the prologue and the road race.