The Witcher 3: Wild Hunt

Unlimited Money (Exploit)

This exploit allows you to earn around 1000 crowns per minute. Take the following steps:

Find the merchant at Hierarch Square in Novigrad and purchase all of his Shells and Sea Shells. Talk to him again after you have depleted his stock and you will find that he has more to sell. Keep buying as many as you can afford and carry.
Take the shells with you and visit the armorer, who is located next to the merchant. Dismantle your Shells to receive Pearls.
Sell the Pearls to the armorer until he runs out of money.
Meditate for 5 days. The armorer should have 1000 coins again. Sell him more Pearls.
Repeat the process as often as you like.

You can dismantle a Shell at the cost of 8 coins for each effort. The Pearl you receive can then be sold for 109 coins. Naturally, this only works during the daytime hours, as merchants aren't around at night.

Duplicate items

Go to any monster nest, and loot everything in the nest except for one item. You can leave any item, but you must leave one item or this will not work. Turn the camera in a 360 degree circle or walk a short distance away from the nest, and then loot the nest again for all items to have respawned. Repeat this as many times as desired. Sell all the items you get from this exploit for lots of crowns. The game has a cap of 65,535 crowns. Thus, stay under that number to avoid losing any crowns. If you meditate for five days, the shops will get all their money (crowns) back. Alternately, go to the Loan Shark in Navigrad since his money comes back each time you leave. You can also buy florens so he has more money, and then just convert florens to crowns at the bank in Novigrad. Note: This glitch was performed on an unpatched version of the game. It will probably eventually get patched. To avoid not being able to use this exploit, either do not install new patches before using this exploit or delete the patches. You can avoid patches being installed by disconnecting from the internet until you are ready for the game to install new patches.

Easy money

Note: This exploit was patched after Version 1.1. Before crossing the Woesong Bridge to leave the town of Midcopse in White Orchard early in the game, jump over the fence to enter a grass pasture with some cows at this location. Kill all the cows at that location with your sword or fire magic. Then, meditate for two hours where you killed them by pausing the game, selecting "Meditation", and advancing the time by two hours. This will force two cows to respawn. Kill the cows again, and repeat the process to accumulate a large number of cow hides, as well as meat for healing. Once satisfied, go to the merchant directly across the road from the cow pasture. Talk to him, then select the "Other" tab from his shop's inventory to find the "Cow Hide" option to sell all of your hides to him. Repeat this process as many times as desired. Note: Since the nearby merchant only has a limited number of crowns, you will need to sell the cow hides to other shop keepers to get more crowns.

Easy XP

Go to the following location in "Velen - No Man's Land", which is southwest of Novigrad. Go under the water (near the wrecked ships), and start shooting at the three Level 10 Drowners with your crossbow to one-hit kill them. After killing the three Drowners, simply turn the camera in a 360 degree circle, and they should keep respawning. They are guarding a nearby chest -- so do not open the chest or the Drowners will stop respawning. If you keep shooting your crossbow towards the Drowners, the game will simply auto-aim at them so you can easily kill them without much effort. You will also need to come up for air when you run out of breath. The Level 10 Drowners are worth 7 XP each. If you are Level 9, you can reach Level 11 in approximately 30 minutes using this farming method. Note: If the Drowners do not respawn, move around a little or turn the camera in the opposite direction to get them to respawn.

Infinite food

Go to the following location at the Clan Tordarroch Forge in The Skellige Isles, and kill all the goats. Next, meditate for one hour for the goats to respawn. If they do not reappear, meditate again for another hour. Kill all the goats again. Repeat this process as many times as desired. Then, loot all the goat corpses to get lots of goat milk, meat, and goat hide. Note: Goat hides are heavy.

Infinite run

While sprinting, jump immediately before your stamina is empty, then release [Sprint]. When you land, your stamina will be full or close to full. A second after you land, press [Sprint] again. If timed correctly, you will not lose your stride.
Extra storage

Use the following trick to store items that you do not want to carry in your inventory. Enter the Inn in Skellige, and go to a corner in the room. Drop all your items at once, and they will appear as a bag on the floor. You can return to retrieve them whenever desired. To add something else to the pile, pick up the bag, and then drop it again after it has the additional item.