There is always something else to carry, I have a 10 metre leather leash and a shoulder lead that is on a breakaway off my belt, Ruudi is brilliant to heel stops to the shot, got no worries with that, when he is close on one he's full tilt he doesn't hold back, I feel better when I have him on the harness and trailer leash. You never know when a road might turn up if you have a runner, the harness is better for a dog by a long chalk against a collar more comfortable and gives you a good link with the dog.
my spaniel works brilliantly off the lead, stops on a sixpence 100% a working dog, but doesn't track like my wire ,you know when he's on it! he won't stop when close to it! harness is essential for my wire! when it's put on, it's like turning on a switch! the dog can do its work without thinking about me and where I am, and I can follow along at my pace, I run him free on tracks, and he ranges for a scent, it's a pleasure to see him pick one up and run into it, but for me harnesses are part of it
if the truck is nearby I use the shoulder lead and collar, I can easily go back on a marker after the shot if needed after 15 mins or so depends on where stalking if I'm on a forestry block miles away from the truck I take the bigger roe sack with the kit with me. Works ok