On the weekend I found out that Randy Couture (and I think Dan Henderson) previously visited my wrestling school and strongly recommended that people shouldnt back bridge for neck strength as alot of “old timer” wrestlers who used this for conditioning were pulling up with bad necks. I understand the american wrestling body (not sure of its name) also advises against bridging except for short warm ups.
As an aside, I learnt 2 odd but effective partner assisted exercises when no weights are at hand (1) partner lies face down on mat - lifter bends over, lifts partner to stomach and then stands up sort of like a bent row + goodmorning. (2) neck resistance exersises provided by partner providing resistance with his hand.