There isn’t really much. The barrier of entry to earn an income online is next to nothing, which is why I’m surprised there aren’t more people doing it.
Computer – Obviously. Get a good one too. While you can technically do everything you need from an internet browser which doesn’t require a speedy computer, you may need to run certain programs to help you along the way, and they can be demanding. I have a Windows desktop and a MacBook, and I use them pretty equally. If you can only pick one and can afford a Mac, get the Mac.
Internet – No shit Sherlock. Fast internet will keep you sane, but anything will do.
Method of receiving money: Preferably a bank account at a large public institution like Chase, Wells or BofA. These banks are more familiar with receiving wire transfers and direct deposits than your local credit union. I’ve had nothing but problems processing payments with these smaller banks, one time I tried to send a wire to my partner and the lady questioned me for 15 minutes about who my partner was, even going as far as Googling me. Mind your own business you creep.
You can get away with only having a PayPal, but not for long because you’ll eventually need to withdraw the money from your PayPal account.
Avoid all other payment processors. Payquicker, Skrill, and Dwolla are cheap, but they’re not widely used enough to be worth the saved pennies.
Functioning brain – This shit isn’t easy. You have to think outside the box, analyze data and trends, and adapt to the dynamic environment of the Internet.
Money itself – Despite what you may think, you don’t need to have money to make money online, it just saves a lot of time.
Credit Card – I’ve gotten away with using PayPal for most of my career, but I have had to resort to paying my Dad to use his CC when I couldn’t use PayPal. Plus, as you grow, you’re most likely going to have some monthly expenses, whether it’s a tool or funding for paid traffic. If you’re going to be paying money out, you may as well use a CC with rewards so you can rack up either airline miles or cash back. NOTE: Never, under any circumstances go into debt for an affiliate campaign if you’re a newbie. Spending money you don’t have, especially on something with high interest rates like a credit card, is a great way to amass debt that will take what seems like forever to pay off.
Separate income source – While it’s obvious that you can be a full-time affiliate after gaining experience, when you’re just getting on your feet it’s not exactly wise to depend on your online income. Having a steady income will give you the cash-flow you need to scale campaigns and take risks that wouldn’t be wise if you were relying in your online income.
Financial savvy – Affiliates that can’t manage their money are doomed for failure. Learn to spend and budget wisely.
Don’t delay starting if you only have the bare necessities, the sooner you start, the better. Experience and information is key, the quicker you can gain those two things, the more successful you’ll be.