The short answer is, none. You can fish with only your hands. There is a long tradition of people feeling around under a river bank and pulling out catfish. Where I live though, in the American southeast, I wouldn't recommend it. People do it, but we have way too many alligators and big snapping turtles, that will bite your hand right off.
When the beginning fisher-person (from now on, I'll use the term "angler to avoid this awkward phrase) enters a tackle shop, sporting goods store, big box store or opens a catalogue, the choice of fishing equipment (called tackle) and accessories is overwhelming. Fishing tackle and related products are a huge industry and a good salesperson will be more than happy to convince you that you can't get started without spending at least a few hundred dollars.... and of course, the more you spend, the more fish you will catch... right? Actually, no. Some, perhaps even most, fishing tackle will catch fish if used properly, at the right time, under the right circumstances and matched tot he right fish. A lot of what you will see though, is designed to catch anglers - they are just shiny lures meant to land your wallet.
All you really need to fish is a few yards of fishing line and a hook. You can wrap the line around your hand or a stick, tie the free end to a hook (by the way, hooks used to be called "angles", which is why people who fish are called anglers), bait the hook with something heavy enough to throw and you will very likely catch a fish if there is a fish there to catch. Hand line fishing works, and in some cases, is a very good option for catching fish. Often times, I catch more blue crabs from the Intercoastal Waterway, with just a length of rope and a piece of chicken than I do with crab pots and traps. I just toss out the baited cord, wait a few minutes and gently pull it back in. If there is a crab clinging to the bait, I'll bring him to just beneath the surface of the water and slip a long handled landing net underneath. As I pull the bait from the water, the crab will let go and fall into my net. You can also fish with a spear/gig or net, but that takes specialized equipment and we will get into that later. For now, lets stick with hook and line fishing.
A step up from a hand line, is to tie a few yards of fishing line to a long bamboo/cane pole. You usually just tie on enough line to reach from the tip (skinny end) to the butt (the part you hold in your hand). This allows you to swing or gently cast your bait more accurately, makes it less likely the fish will see you and the flexible but strong cane pole gives you leverage to land the fish. Hand lines are better for smaller fish, because they lack this leverage - fighting a larger fish can cause the line to cut into your hand. The flexibility and resilience of the cane pole also allows you to use lighter line. Lighter line is less easily seen by the fish and allows the bait to have more natural movement int he water. I have landed many 15 - 30 lb catfish with only 10 lb test monofilament line on my cane pole. "10 lb test" means the line is strong enough to suspend 10 pounds of static (not moving or jerking) weight. Even though fish jerk and jump as you try to pull them in, the springiness of the cane pole and the slight elasticity of the monofilament, make landing a larger fish no problem (so long as you are patient enough to fight and land the fish, as opposed to trying to yank him out of the water as soon as he strikes your bait).
This simple set up only needs two (optional) improvements to maximize its potential to catch fish. The first is a small metal weight or sinker that you can tie near the hook to help it sink. The second is a bobber or float. The bobber serves two purposes, the most important of which is that can be used to control the depth at which your bait is suspended in the water. The bobber is tied or clipped onto the line - the higher you attach it above the hook, the deeper the hook hangs down n the water. The bobber can be used to hold your bait just off of the bottom mud, dangle it just above under water weeds or just below the surface. The bobber and the weight allow you to put your bait where the fish are feeding. The second use for a bobber is to indicate a strike. The bobber is colorful and floats on top of the water. When a fish nibbles your bait, it will shake. When a fish takes your bait, it will dip under the water, telling you to pull back and set the hook.
A cane pole, a few yards of line, a few hooks, sinkers and bobbers are all the equipment you need to begin fishing. The total cost of this outfit should be less than $10. All you need beyond that is bait, a fishing license (if necessary - check your state fishing regulations) and a body of water. One dinner of fish will more than make up for your monetary investment. So, there is really no excuse not to take up fishing in 2016. The season will soon be upon us!