I have osteoperosis, so I wear more than most, doesn't take an awful lot to break me. So, kyle strait knees, except for the most basic and undemanding of dull XC.
Elbow pads most of the time- I did have a set of 661 Chicken Wings which are small and seemed ideal, but turned out to be uncomfortable, sweaty and very restrictive. So now I have a set of POC Bone elbows, which look ridiculous- very big, and bright white- but are much less enclosed, so they're less restrictive and much less sweaty despite their huge size.
Sometimes 661 Evo armoured shorts. I'd wear these all the time but they're a bugger to wash because of the custard!
And the usual, helmet, gloves, and often glasses.
Thing is, with all of these they're no bother to ride in. I wouldn't want to make sacrifices for protection but the Kyle Straits and the shorts make no difference at all to how I ride. The elbow guards to a little but it's trivial.