I find I use all sorts of gear I have accumulated over my 22 year USAF career. When compared to commercial gear, mil-sec is generally heavy but very robustly built. Some of my favorite and most frequently used bits of kit include my Cammenga Tritium Lensatic Compass (ballz accurate&bomb proof), P-38 (can opener, not Range Rover), flyers kit bags (super robust& flexible duffel), Wolf Boxes, 3 day assault packs (ditch bag), ever trusty DCU pants and my favorite cool weather piece, the liner from a Gortex ECWS. I think the best kept secret in Military issue is the "Sleep Shirt", NSN 8415-00-890-2102. It is 100% polyester, heat retentive, moisture resistant, quarter zip garment. BUTT UGLY, but effective! It is my go to garment when there is a chill in the air. I wear them for outdoor work, camping or any other physically oriented activity where you have varying conditions. The sleep shirt has been around for about 20 years and is IMHO quietly a premier high performance layer.
I would not recommend hitting the field in full surplus equipment, however I don't hit the field without a smattering of Mil-spec items that have either proven themselves or that I am comfortable using. Economics plays some part in most of our gear decisions. My "can't live without" Sleep Shirts have their equals on the rack at REI but at $75 or more, the considerable aesthetic advantage the Mountain Hardwares or Arc Teryx's hold just isn't worth the considerable cost to me when function is equal. Most everyone on this forum is very selective about the gear they use. Unless you are a deep pocketed ExPo fashionista, have solid sponsorship deals and/or a distaste for less than state of the art, you can find some very high functioning, high reliability items for your personal kit that have been proven by the greatest military history has ever known. Who couldn't save a buck here or there as long as the gear adequately meets your requirements? When selecting gear, some Mil-spec items may meet your criteria. I don't think surplus Military gear can be totally discounted as possible source, you just need to analyze it against your needs.