There's almost no limit to the ways you can make money, but most of them require work (that particular balance is known as "the human condition"). However, there are ways to make extra cash without going too far out of your way. Here are a few.
A small disclaimer that should go without saying: nothing in here is going to make you rich or pay your bills. The idea is to make a bit of extra cash while you idle in the checkout line, in awaiting room, or without doing anything at all. With the exception of large capital investments or owning a business, most things won't make you a ton of money for that little effort. However, a few extra bucks here and there is still something, and if you add up everything here you could give your petty cash fund a nice pad. If you want to put a bit more effort in, there are plenty of ways to make even more money in your spare time.

Get Paid for Answers with Google Opinions and Other Surveys

How to Make Money Doing (Almost) Nothing
Recently, Google released a new app to the Play Store called Google Opinion Rewards. The concept is simple: answer a few questions every once in a while and get some free credit for the Play Store. It won't be much, but the app will send you a notification when you can fill out a new survey and they're typically only a few questions long. Within thirty seconds or so, you could get an extra dollar. That's a return on your time investment roughly equal to making $120 per hour.
Of course, if you don't have Android or simply prefer real money to Google Play credit, there are plenty of other services you can try. CashCrate is another site that pays money in exchange for filling out surveys that can be done within a matter of minutes. As with Google's version, there's a limit to how much you can make with surveys alone (and there are other, moreburdensome options like completing offers that will attempt to suck you in further), but filling out one minute surveys once a day or when they pop up can still accumulate actual money if you're diligent.
If you're looking for sites that you can perform quick tasks to earn a bit of money, here are a few of the legit ones. While individual tasks can be quick, it's also up to you to not let it take up your time if you want to keep to the minimal effort goal:
There are, of course, some things you should be aware of when pursuing sites like this: for starters, not all of them are going to be legitimate. If you try to turn answering surveys into a full-time job, it would be easy to find yourself on the business end of a phishing scam. Just accept that it's a buck or two here and there and you'll be better off (and if you do want to take it further, know the right ways to do so). Secondly, these things are only viable because somewhere, some focus group or marketing machine needs data to drive its decisions. It's very obvious to see why Google would shell out a pittance for data on consumer habits. If you're okay with this then fire the app up, but if you don't like the idea of a company having even anonymized data from you on its servers, you should probably sit this out (and by "it" I mean both paid survey apps and, quite possibly, the entire internet).

Make Money While You're Out with Apps Like Ibotta and Gigwalk

How to Make Money Doing (Almost) Nothing
Couponing is a lot like most hobbies. If you really want to get enthusiastic about it, there's almost no limit to how deep the rabbit hole goes. However, you don't have to go all out and turn couponing into a full-time job if you don't want to. Apps like previously-featured Ibottaallow you to pick up a few cents here and there during your regular, everyday shopping. Ibotta will show you a selection of items that have deals available for them. Some of the deals require you to complete a quick survey or even "learn a fact" which is, essentially, just tapping "Okay" once. After that, you just have to scan a picture of your receipt to claim your reward.
Gigwalk can be used on a similar principle, checking for nearby "gigs" that you can complete for cash. Retailers sign up and enter tasks like auditing a display or checking to make sure things are in order. You can think of it like bite-sized secret shopping. The great thing is that many gigs are available at large retailers like Walmart, so if there's one available at the store you're already going to, you can make an extra few bucks just by stopping by the electronics department.

Use a Credit Card with Good Rewards

How to Make Money Doing (Almost) Nothing
Credit card companies will be all too happy to tell you how wonderful their rewards programs are and, in general, you probably shouldn't take them at their word. However, that doesn't mean that there aren't credit cards with some actually good rewards! It's hard to go wrong with simple cash-back rewards, even if the return isn't huge.
When it comes to maximizing credit card rewards, it's not terribly difficult. Start by getting a credit card with good rewards, and then use it for things you're already planning to buy (and be sure to pay it off immediately). While this is the no-effort method, you can also turn up the bonus a bit by purchasing gift cards for stores you'll shop at anyway since many credit cards will pay more rewards for purchases at grocery stores that sell gift cards than for those stores themselves. Once you've accumulated your rewards, it doesn't hurt to know how to spend them wisely.