Hmmmm, that is tough for a dog gear addict, LOL...
1 good harness
1 leash (if I had to pick one, I'd pick a tape Flexi since it can be used in multiple situations - so that he could have his room to run on hikes but stay safe and then be able to lock it when needing to stay close)
Food/Treats (is that 2 things? lol).
Back to basics I guess.