For imprisoned activists and prisoners of war, communication with the outside can make a world of difference, keeping them informed, reminding them that they haven't been forgotten, and simply easing the boredom of incarceration. http://denverabc.wordpress.com/political-prisoners-database/ contains a list of political prisoners held in the US (obviously there are political prisoners in many countries, but this list is just for starters).
Several websites have guidelines for corresponding with prison inmates. A short-and-sweet version:
1) Find out from the prisoner and the prison authorities what the rules are there.
2) Use a return address. This can be a post office box.
3) Be careful about saying anything that touches on illegal or otherwise sensitive matters.
4) Don't be disappointed if you get a delayed response or no response at all.
5) Be cautious. Don't send money or things you can't afford. Don't give financial information.
6) Don't give false hope.
7) You're interesting too - tell the addressee about yourself.
Effort involved: writing a letter takes a bit more work than writing an e-mail, of course, but that's part of what makes letters more personal. Also, you just may end up writing to a future president of the Czech Republic or Brazil, which would be a cool thing to bring up at dinner parties 20 years down the line.
In this era of rampant e-stalking, being able to easily find the contact details of old acquaintances can be used for good as well as evil. For instance, you can send a teacher - anonymously if you have a fear of social interaction - a belated thank-you. This doesn't have to be a high school history teacher or a college writing professor; it can be a coach, tutor, the family friend who taught you to play the recorder, or the neighbor kid who was the first to show you how to ride a skateboard. As supremely talented and perfect as you are, you most likely didn't spring forth that way from the womb. So it's a nice gesture to thank someone who was influential, in however small a way, during your formative years.
Effort involved: a few minutes to look up an address, a few minutes to write a note. Simple!
Image from http://www.metro.co.uk/weird/332755-skateboarding-dog-is-a-web-hit
Food waste is inefficient both environmentally and socially, as overconsumption (through waste) by the wealthy often drives up food prices for the poorer, making basic foods less affordable. One way to combat food waste is by getting together with a few friends, neighbors or colleagues and agreeing to place all food that will go bad soon in a communal space or listing these items in emails. This is a great way to get rid of food that can't be given to food banks or other organizations because of open packages, very small quantities, etc. And everyone in the group gets to try new food for free, which is a definite plus.
Effort involved: not much, really. This group can be as informal as you want, e.g. just leaving some of that ridiculously large bag of cinnamon you impulse bought on a table at work, then watching bemusedly as your free-food-whore coworkers swoop down on each fresh addition.
www.change.org is full of petitions ranging from the serious to the frivolous, and the perfectly logical to the totally incomprehensible. I defy you to find one that doesn't strike a nerve in you.
Effort involved: very minor. A little clicky-clacky and a bit of typing - that's all.
Most likely the office manager will be pleased to be able to put out new reading material (which is old to you). You get to declutter, and the experience of waiting for a doctor or dentist gets marginally less horrible for those doing the waiting (even if, for some, one of the few pleasures of visiting a dentist, doctor, etc. is skimming through decades-old publications they'd be embarrassed to have in their own homes).
Effort involved: only as long as it takes to load up some magazines and find a waiting room. If you're reluctant to talk to people inside, you could always anonymously leave them outside.