I recommend asking them where their problem areas are. It can differ greatly from cyclist to cyclist, and also from ride to ride.
My husband is a cyclist and I have worked on him (as his personal, dedicated MT!) for races and events. What I usually do post event is work the legs over briefly, but somewhat vigorously and with swedish techniques - petrissage, tapotement, effleurage, etc. on the quads, hams, and calfs. Then I ask him what else he needs - and it has varied from his shoulders to neck, to feet, to different areas of his back
Also, note if you are working on Saturday, do they have another ride on Sunday? You don't want to do any serious trigger point or deep tissue work if they need to ride tomorrow, at least on their legs or core muscles. Trigger point on the neck/traps is probably fine and useful, because as Ella said, the neck can be a serious area of tension, esp. for longer rides. Also, if they are doing a Time Trial and need to be bent over in an aero position, they can develop pain in various areas of the back, depending on the position they hold. Ask them about their back because some cyclists have the pain very high up between the shoulder blades and others have it lower down.
Have fun! Events are a blast. Let us know how it goes.