I know you have all been waiting patiently to see what I endorse...
On most rides, I don't throw on additional padding (standard kit = baggie shorts with padded liner, jersey, helmet, glasses, full finger gloves and usually a hydration pack. Oh shoes and socks too) - but I usually carry my forearm guards, and I don them for rides down The Luge, 5-Oaks, etc.
I need my forearm/elbow pads. That's where I fall when I fall. I hit my forearm on virtually every crash - often as a function of a tuck and roll. I rarely hit my knees.
If I am doing an assortment of hard trails, and/or if it's cold out, I will wear some manner of knee protection along with the forearm guards. I have three different sets of knee protection from Race Face padded leg warmers to IXS hard-shell knee guards. Come to think of it, I have full length IXS knee-shinguards too - but only when shuttling or riding park.
I use a full face and goggles when shuttling or riding park. NEVER wear a full face and sunglasses. That's just as dorky as wearing goggles with a half-lid.
I have seen a steadily increasing number of riders doing very mundane and easy trails with full-face helmets. Whatever makes you feel better.