Yay, the last one! Writing 24 blog posts in 24 days is a lot more work than actually contributing 24 times. Let's go over the different things that I managed to accomplish, and what you can do to continue some of that work yourself.
A few of my contributions are related to PHP's DateTime support. On the 6th and the 9th I wrote about a bug fixes in "Cookie formats" and "Day of the week" calculations. The bug reports (#61599, #63391, #63776 and #64294) mentioned issues all came with a good reproducible script. Please continue filing bug reports, and make sure you follow the guidelines (if possible/necessary) from the 23rd.
The other DateTime issue that I touched on the 21st is probably something that you can't really contribute too—unless you want to start petitions and lobby to get rid of Daylight Saving Time altogether…
I have been working on and off on Xdebug for about 13 years now, and it is still a project I am very interested in. So it could not have come as a surprise that there were four posts about it. Some of them, such as on the 1st ("Xdebug and hidden properties)" were helped by a good bug report. But there are plenty of more bugs in Xdebug. Some of them I can easily reproduce, others only with difficulty and some bugs are just weird. Going over the bug list of your favourite project and trying to reproduce and clarify them is of great help to project maintainers that do not always have a lot of time themselves. In some cases, they might not even have access to the same platforms (ugh, Windows) as what the bug report was filed for.
Other ways to help an Open Source project is by answering questions on the project's mailing list, or on IRC as I did in the post on the 8th. Project maintainers are not awake 24 hours, and especially if you are in a different timezone, your knowledge can help other people. I often lurk in channels on IRC to help out on Xdebug, PHP, OpenStreetMap and MongoDB.
And of course you can contribute to Open Source projects by just submitting pull requests like I did for the 15th and the 20th. Most projects will have guidelines on how to contribute. For example Xdebug has a contributing page, and the MongoDB driver for PHP has a page on GitHub.
Another large group of contributions (7!) are related to OpenStreetMap. There are many things you can do yourself to help fighting commercial monopolies on geographic data. Two of the posts on OpenStreetMap (on the 2nd and 10th) dealt with ITO World's OSM Analysis. This tool highlights differences between Ordnance Survey's OS Locator product and OpenStreetMap. If you are in the UK, why not have a look if there are any errors near you? For example, in Manchester there are 189 discrepancies right now. If you don't know how to get the right data into OpenStreetMap, take a (geolocated) photo of the street sign and add a link to it in an OpenStreetMap note. Please do not just believe OS Locator's variant of the name, or copy any data of any other map. The only thing that will suffice is proof (a photo) that the name is different. In some cases, you might of course need more photos as I showed in the post for the 16th.
I posted an article on OpenStreetMap notes on the 5th. Notes can be posted anonymously but then we see the text "This note includes comments from anonymous users which should be independently verified." You can sign up as an OpenStreetMap user, where it will be explained that you can never copy data from other maps, but a nice photo of a street sign is of course good enough as well. You can also add comments to notes as a user, and if you sign up as a user, then you can also add and modify the rest of the map like I demonstrated on the 19th.
The last group of contributions that I want to talk about are for your own project. I do lots of little things here and there, for example with the geospatial extension that I wrote about on the 12th. In my opinion there is nothing more fun that to hack on your pet project. However, sometimes that results in a project that you work on for 12 years (Xdebug!), so be warned!
Merry Christmas, and I hope this series of posts inspired you to make your own contributions. Perhaps make it a new year's resolution!