In order to make things easier, I would actually recommend you to always have a stash of all resources, just in case. Keep the basic ones - like Oranges, Flour or Linen Cloth at 20, while trying to always build up the stored amounts of all the others for faster progress. You will see that you will need a lot of certain ones - like Heartwood Fragments - so always adapt and keep a stock of items you need. Tap to collect from the different battlefields
Your hunters won't collect all the loot that's dropped by the monsters they defeat - but that's a good thing, as you can collect it instead and get all those materials for free! Just go over the battlefields every now and then and collect all the shiny items there. Keep an eye out for Elementals as well, since tapping them rewards you with items you can use to purchase various boosts.