I donate $100 per year to Linux Mint, the first around Memorial Day, and just after Thanksgiving, so that Clem will be able to provide support when many are spending for the Christmas holidays.
What I don't do, is 'support' Linux via purchasing DVD's though OSDiscs(dot)com, yes that may donate, yet it's off of any profits of the purchased media. If the one running the show has makes no profit, then the distros gets nothing. Note that with most Linux OS's (based from Ubuntu), there may be a pop-up at boot, with a donation link, of which 100% goes to the maintainer, not via a 3rd party getting a third to half off the top. It's always best to donate directly to one favorite or most used distro (other than Ubuntu, Canonical is a for profit corporation that rakes in boatloads of cash per year, otherwise wouldn't have offices scattered all over the globe.
I agree with Rocky on supporting the Free Software Foundation, which is actually a non-profit, and works hard to get the word of Free Software to the masses. If there's been anyone in their life who has contributed the most to free software, like him or not, it's been Richard Stallman. KInd of like (the late) Steve Jobs & the Woz, the latter done most all of the work & Jobs got the credit, as well as fame. Had there been no Richard Stallman, there would be no Linux as we know it, that would had left Linus Torvalds to come up with a dozen years of work that Stallman had already completed. Linus took his work & only needed to compile a bootloader (what Stallman couldn't do) & gained all of the fame.
So every now & then (no schedule), will make a contribution to the Free Software Foundation.
If Canonical were a non-profit, then I'd contribute, what we get in free Ubuntu is the base for customized distros for governments, the financial world, schools, healthcare & more. All of these pays their way, which allows for Canonical to be financially able to distribute Ubuntu. It's founder & former CEO is a certified millionaire.
Among his hobbies, he paid a huge sum (in USD) of $26.63 million (adjusted for current dollars) for a trip in space in the International Space Station back in 2002. Seriously, I don't believe he needs nor deserves any donations, he's raking lots of cash in for professional support, which most any Ubuntu user can sign up for, as a yearly subscription. It's the competing distros not as much in the spotlight that needs the cash more & wouldn't be blown on luxuries, rather being able to hire their own staff & having to make every dollar stretch as far as possible.
This is why many distros also invites those who wishes to code, perform artwork & work on other projects just as much as cash donations. If these were paid coders & their work was used to further develop the distros, would be far more worth than a $50 donation alone. Linux users can also help simply by spreading the word........not simply handing out a DVD as though a flyer, rather working one on one with folks that wants to learn a Linux distro. Place your phone number (or email address) within the DVD sleeve, and try to work with many as possible, as time permits.
Last month, I got two elderly ladies off of a sluggish Windows 7 & onto Linux Mint MATE 64 bit, which compared to W7, screamed on the notebooks with dual core Pentiums. One wanted more speed, so I suggested a SSD & max out RAM to 8GB (the 'sweet spot' of today), she told me to pick those out that would be the right for her & she'd order it, and she did. We then fresh installed Linux Mint 18 on a new 250GiB Samsung 850 EVO & with 4GB extra RAM, was super fast.
What did I ask for in return? Not a red cent, and told here that I was a phone call away if she needed assistance. Two days later, she called, and stated that he computer needed looking at, and guess what? It didn't need anything, she baked me a fresh pound cake, and gave me a small box, though asked me not to open until I had returned home. In it was the original 4GB (2GB x2) OEM sticks, each in a small zip lock bag that at some point, will use on another's computer. This is how the Linux Community should work, and in some areas, does.
I later called and offered to install a i3-370M that would had been a drop in fit & features H/T for free, although she was pleased with what she had, stated if the notebook were any faster, she wouldn't be able to keep up.
Also called the other lady, she was still as happy as could be, and when the season was in, I'd get some fresh veggies, which I still get from those I assisted from years back, as well as backed goods, homemade jelly, an occasional ham or deer shoulder & various computer equipment (to include complete units). it simply feels good to contribute to the local community when I can, while I ask for nothing from these folks, have made a lot of friends over the years.
So giving back to Linux doesn't always involve cash, most anyone can easily give a few dollars & forget it, I feel that my local contributions far exceeds what I've donated to Linux Mint, that is, if a monetary value can be placed on assisting others in need of freedom & out of despair.