Re: 5/3/1 BBB Question...
I've always made the accessories the opposite movement of my main lift for that day. So if my main lift is a push (squat), my accessory is some kind of pull (deadlift variation). Since both upper-body lifts in 5/3/1 are pushes, I'll usually use something like Pendlay rows, or pullups as accessories (unless I've hammered pullups in WODS all week). I've also used cleans as an accessory pretty often.
It's win/win for people who are also doing crossfit, in my opinion, because it allows you to get a little more frequency in your programing than you otherwise wouldn't get from strength-focused lifts that aren't part of a metcon. It also doesn't leave those muscles too shot over the next couple days, allowing metcons to be added in. Doing 5 sets of higher volume squats after lifting heavy on the same movement is going to have a pretty significant effect on recovery time. Might as well split it up.