3 trikes - 3 answers
Trike used generally for touring has a large rack just above the axle. Lights fitted to carrier.
Trike used for hack or general use has a Longstaff saddle bag support which clamps to the saddle pillar. Same supporting effect as the support (name escapes me for the moment) that clamps to the saddle rails. Lights fitted to seat stay but could be on the carrier.
Hack trike has a Karrimor uplift to drop into the saddle bag loops on the B17. Lights on the seat stay.
Excluding option 1, the possibilities for bag support and light mounting is really the same as on a bike.