Whenever you find geyser, dig the area around it until it is covered by water. Mark it on your map. Whenever you pass by the area the surtlings that spawn there will die instantly from water damage, dropping sturling cores and coal. If you can find 3 or more geyser near each other this can replace charcoal kilns entirely.
Craft an iron Mace. Most enemies in the swamp are either weak or neutral to it (including the boss) and it will serve you well even in the mountains later against golems.
The only blunt-resistant enemy in the swamp is the abomination, you gotta use slash weapons on it.