The Banner Saga 2

For this achievement, you need to keep careful track of how many days worth of provisions you have. There is never any guarantee you'll get a random encounter to help you along the way, so try not to leave camp without a good ten days worth of supplies. That said, any random encounters you do come across, choosing an option that will lead to extra supplies is always a good option, unless there is one that will lead to a battle. Battles are more scarce than supplies, so focus on those for Warmonger.

One thing that will help this is making sure you do not train your clansmen to become fighters. Fighters are worthless as they will use up more supplies, and your clansmen will forage on their own every few days, so it hurts twice as much. You need to get 600 fighters for another achievement, but you can do so and then reload a save to keep your clansmen instead.