So the way to grind optimally seems to be to train once in the morning, then if you need water go to forest. Make sure to save. If you don't need water, train second time. You have now entered afternoon, unless you are absolutely fucked on health, save and get food, you can't train, you can only go to sleep to recover health. The drop rate has increased because now in addition to trees there are treasure chests and the first time it unlocks agility training (not quite sure what it does, it doesn't seem to affect dodge but maybe it's very minor), but after that they contain bananas (doesn't make sense why an ancient pirate would store bananas, the most notorious fruit that would definitely rot, but fuck it).
I feel like the river is less hard to find now? I feel like it should just be stationary, and it feels like I always find it when I go left, but never in the exact same way. Also don't throw away water bottles, I don't think you can get them back and after finding food, I threw away three.