On alpine rock routes, you are going to be wearing a pack. Even on longer one day routes from basecamp, at least one pack (maybe carried by the second) is usually needed for water, munchies, shoes for the walk off, and maybe a cap or windbreaker. But one of the Big Hassles with wearing a pack is that the waist belt can interfere with accessing the gear loops on your harness.
Counter this by adding two loops of cord onto your pack shoulder straps. I think I used 4 mm, the stiffer the better. Buy 5 feet of cord total, 2.5 feet of cord for each loop. (Yes, you’ll have a bit extra, but better too much than not enough.) Brighter colored cord is easier to see at a glance. Tie the cord into a solid double fisherman’s knot, dress it well, and tighten is as much as you can - pliers can help here. If the knot tails are long, you can wrap them with athletic tape to keep them out of the way.
You want the loops to generally hold their shape. If they’re too floppy, stiffen then by wrapping with electrical or duct tape.
One more way to make the loops stiffer: Buy 1 foot of clear plastic tubing from the hardware store, cut that into two 6 inch or so lengths, and thread the cord through the tubing.
These shoulder strap gear loops are a super handy place to keep your rock pro, a few extra biners and a nut tool, without fighting to get at the gear on your climbing harness hidden by your waist belt. Also, when cleaning a pitch as a second, it’s a fast and easy-to-reach place to clip gear.
Some climbers may rack snow pickets and ice screws here as well. But, keep in mind what this sharp flying metal in close proximity to your face might do to you if you take a fall. Your call.