I wear knees & elbows for pretty much any ride off-road.
I've found on easier trails it's more my forearms that get hit - eg. getting careless and too close to trees in tight singletrack, which is not enough to crash but enough to take some skin off my forearms.
There are some TLD elbow guards that have a semi-hard shell and go all the way down the forearm. I'm onto my 2nd pair and am pretty happy with them.
http://www.chainreactioncycles.com/au/en/troy-lee-designs-egl-5550-elbow-forearm-guard/rp-prod59942
As with knees, they make everything hotter & sweatier but I'm happy to live with that even in summer instead of the irritation of long bloody abrasions down my arm.
And goggles at bike parks etc or wherever it's very dusty. Otherwise glasses.