I personally have enjoyed working a direct sales/home based business on the side. I found a good, legitimate company with very low upfront costs/overhead. It has been a great experience. Just be sure that the company offers training and some sort of simple, step-by-step system and it helps if they are in the DSA Top 100– instantly proves their legitimacy!

No one knows your hometown like you do, and you can translate that into cash by leading tours of your city. The website vayable.com allows you to set up and guide tours around a particular cultural experience. Are you the foremost expert on ghost stories, beer, architecture, or crime (or anything else!) in your town? Then you can start leading tours for people who want to hear your stories!
25. Products – You can create your own product, such as an ebook or computer software. You would then use your blog as a promotion tool to get people to buy your product. As long as you create a legitimate product with a whole lot of value, you should be able to get some buyers, but like everything else with a blog, you’ll need the traffic to get the sells.
Buy and sell domain names. If you’re good at finding popular yet undiscovered domain names, you can make some cash on the side by buying and reselling websites. Think of it as digital real estate speculation. Domains are available on GoDaddy.com for as little as $2.99 per year, but are sometimes resold at far higher prices: According to Business Insider, the site MM.com sold for $1.2 million dollars in 2014. Once you find the perfect domain name to resell, you can market it on Flippa.com for a flat fee.
According to Getaround’s estimates, car owners that routinely lend out their car can earn “$1,000s per year actively sharing your parked car”. Considering there is no effort needed by you, it’s a pretty good way to make money. That being said, your car will likely depreciate a bit faster by virtue of lending it out to other people. If you have a big car loan or are underwater on your loan, putting your car on a site like Getaround might not be a great idea.
The stuff you can’t sell online, you could sell from your garage on the weekends. Many neighborhoods plan annual or bi-annual yard sales. If you have items to sell, this is a great time to do it as the neighborhood as a whole can bring in a lot of traffic and help you perform better than you would on your own. If that’s not possible, consider partnering up with a couple of families in a popular neighborhood.
I’ve tried a fair few things on this list and I’m a big fan of those side hustles that have the potential for ongoing passive income once you’re set up. For me, the most successful have been blogging and T shirt designs (I use Merch by Amazon but want to look into Teespring as you suggest). I’m currently working on an Etsy printable business, again for the passive income potential!
@moxie1956 Thanks for sharing your experience with CashCrate.com. That’s certainly disappointing to hear that you weren’t able to make the $50-$75 a month that I expect. Maybe they are just going through a seasonal downturn or something. Like I mention above though, the real money with Cash Crate comes in the referrals. Find a way to consistently refer a large amount of people to the site.
Worth noting is that Postmates doesn’t even require that you deliver by vehicle — a bike will do.  Better yet, there are no startup fees or time commitments with Postmates and all you’ll have to do is pass a basic background check to get started. Once Postmates verifies your identity, they’ll send you a delivery bag and a prepaid card (in the mail) that you’ll use to purchase delivery items.
It’s industry standard to charge anywhere from $1,000-$2,000 per month per client, and you don’t need previous website or marketing experience to get started. As you bring on more clients and build a reputation in your community for delivering outstanding results, your income can scale up quickly. It only takes a handful of clients to start building a full-time income.
Research Pricing (And Set Fair Starting Prices): Before setting prices for each item, research your local Craigslist website and (if possible) nearby yard sales to get a sense of how to price them. Remember that many buyers will try to haggle – so set prices a bit higher than your bottom dollar, but not so high that you’ll scare off first bids. 10% to 15% is a good rule of thumb. Consider bunching low-value items, such as old CDs, into lots of five or 10, or offer x-for-$y deals.
If you're running on fumes, financially speaking, but you have some money coming your way soon, consider pawning something of value to borrow fast cash. Of course, to get those items back you'll need to pay back the loan with interest. If you don't pay it back in time, that you'll lose the item. If it's really something that has a lot of intrinsic value to you, don't do it. But if it's something that doesn't, you can certainly consider it depending on your situation.