Learn about repair first, then by tools and supplies. The odds of needing a shift cable on a bike less than a year old is next to zero, but it weighs almost nothing, so no great loss to carry one. Brake cable is even less likely to be a problem, but go ahead if you insist. I did a 5000 mile tour in '76 and indeed needed to replace a shift cable, but the bike was 4 years old with thousands of miles on it.