For the biggest turnout, you need to know people's preferences: when, where, how much, and for how long. You need to offer choices though, "or you could end up with as many different days and locations as people you polled," Clunies says.
To come up with the options, consult key family members who either must be present (say, grandma and grandpa) or are the link to many others (e.g., your sister who has four children and nine grandchildren). Once you've done your research and collected everyone's e-mail address, create a survey at Surveymonkey.com. The website will e-mail everyone a prompt to take the survey and tally the results (it's free for 10 questions and 100 responses). You can also send the link as a text to cell phones.
Announce the date, place, and other pertinent details as soon as they're set. If it's more than a few months away, send out save-the-date notices requesting that people pre-RSVP so you can start booking the space and accommodations needed. Many sites allow you to e-mail invites and notices and will track responses: MyEvent.com and Eventbrite.com will also help you collect money (for a small fee, including credit card processing charges); at PaperlessPost.com you can have the invites printed for the technophobes in your family.
On the survey, ask how people can pitch in. "The more help you enlist, the more people there are who have ownership of the reunion and want it to be a success," says Edith Wagner, editor of Reunions magazine. There's also a ton of stuff to do, including creating a Facebook page or blog (if you so choose), arranging an account at Shutterfly.com or Flickr.com so everyone can easily share their photos, and printing copies of the family tree that can be passed around to be filled out (find free templates at FamilyTreeTemplates.net).
Managing the whole crew without losing your mind is possible with an app like Wunderlist (Android, iOS, PCs, and Macs), which lets you create to-do lists, send and assign tasks to your team, and be notified when people check them off as done (the free version allows three assignees in the beginning and then one per day; for more, the cost is $4.99 per month).
The abundance of online custom-print places makes this affordable and fast; in addition to t-shirts, you can order in bulk baseball caps, shopping bags, scarves, you name it. But don't spend more than $10 per person, Wagner recommends. "Some people will use their souvenir till it's in shreds, others will never touch it again, so you need to balance those two attitudes by not spending too much or too little money," she explains.