Stock and handguards are a big part of it. Not having a bunch of unnecessary stuff attached is a big part of keeping it light. Barrel is probably the easiest place to save weight, but it's also probably the biggest factor in overall accuracy, so choose carefully. You can save a few ounces/grams here and there by paying attention to which upper, grip, bolt carrier, gas block, etc. you choose. Which sights/optic you choose makes a big difference as well. Remember, weight near the muzzle feels a lot heavier than weight near the buttstock.
If I were really going for weight, and keeping to a tight budget i.e. not just buying a bunch of skeletonized or titanium parts, I'd probably stick with the Minimalist stock, go to a 14.5" barrel with a pinned/welded flash hider or lose the flash hider and just get a thread protector instead, use a smooth-side upper, and maybe get a shorter handguard. No slings, bipods, flashlights, back up sights, extra rail sections, etc. If you're really concerned about weight and don't plan to be too hard on the rifle, consider a poly lower instead of aluminum.