For location finding and tracking rides made: maps and strava on phone.
Used to have computers on the bikes for cadence and speed, but ditched them when they got buggy (batteries draining too fast, loosing cadence, getting stuck in the wrong mode, etc.). I have zero tolerance for malfunctioning electronics and am not amused by gadgets.
If I ever find myself participating in unfamiliar cue-sheet rides with a regularly rotating paceline again, it might be nice to have something that shows the highlighted route in real-time, so I could take my turns at the front with confidence (can't follow a cue sheet while riding to save my life), but a bar-mounted GPS unit aside from that? No thanks; I'm not in a submarine!