The bare minimum I have used to catch fish is a string and a hook with whatever insect or worm I could find crawling around. Some people fish with their hands and are very successful. Some tribes in my area are allowed to use spears and/or nets.
You don't say what kind of fish or fishing, deep sea fishing, or freshwater fishing. For freshwater or shore fishing, the commercially available starter kits or pocket fishermen rods are a decent start and contain the common equipment of a rod, reel, line, assorted sinkers and weights, lures, hooks, eyelets and bobbers. Large fish and deep sea fishing require more specialized equipment.