You can split stacks; hold shift when clicking on them.

You can fish, but it requires you to:

1. Have Gold Coins.
2. Find the Trader in the Black Forest biome.
3. Buy both the Fishing Pole and Fishing Bait from him.

You can get Gold Coins from:

* Killing Trolls and out of Troll Caves
* Burial Grounds (in chests and lying around)
* Killing Fulings
* Other Chests

Also, the Trader will buy items from you, such as:

* Gemstones (Ruby, Amber, Amber Pearls)
* Silver Necklaces