Yes, the 156 has cruise control. It was fitted to all models, but the stalk was omitted from some, so needs to be added by you & me. Not a hard job. 80 pounds for the parts.
Fuel computer is included; shows consumption and anticipated range. Works alright.
Outside temp gauge is included in the onboard computer.
There have not really been many accessories thrown into the 156. Only check if the spare wheel tool kit is full, and the manuals, and both keys are present. Keys cost as much as 200 pounds to make, so be sure you insist on them
Anyway, good luck with it
2003 156 GTA Selespeed - Alfa Rosso + black multispokes, Eibach anti rollbars, Quaife ATB diff, 330mm brakes, Bilstein B12, De-cat wrapped manifolds + EQ downpipes + Ragazzon silencer, CDA intake, (carefully) removed interior & Sparco bucket seats + 6 point harness