+1 for ear plugs! My own band never gets so loud that I would need them, as I have a sensible and loud-phobic drummer, and I control the PA. I keep a pair of ear plugs in my gig case, and I have them to hand when depping or rehearsing with other bands. I have another pair that I can take to gigs that I'm attending.
I suffer a bit of distortion in my right ear that I got from sitting in front of the PA at a gig many years ago, so often I just put the right plug in. I favor Doc's Pro Plugs btw. You need to find the right size, but once sorted they are comfortable to wear, you can still carry on a conversation, and they don't make you look like div (but I would still use them if they did).