If possible, keep all the iDevices OFF while at home. They will almost always be contacting something on the web, try to allow that only when you have to.
Obviously, whenever a Desktop browser or your iDevices are ON, they may be updating info or refreshing pages, even when a tab/window is open. On the iDevices, it can also help to completely shut off an app, rather than simply going to another open one. Just because an app is not visible doesn't mean it is not 'talking' to the Mother Ship or the sources it uses for displaying info.
Lastly, if at all possible, make all your software updates at a secure WiFi location, that will be one that has password requirements. Barnes & Nobel/Starbucks/etc. don't count. An Apple Store would be great, of course, those are not always close to "the sticks"... Even better, try to find some one closer to "town" with a wired connection to the web and become their friend! Do you make delicious cakes/cookies/lasagna/etc.?
With the updates to the iDevices, remember you should be able to do that while they are connected to the MacBook through iTunes. That way you may have faster download than with the iDevice alone.
OTOH, being far from the maddening crowds has certain benefits...
Install Adblock on all your browsers - and reduce the amount of data (some ads are animated/video etc. which will use more bandwidth than just the web page in some cases).
Make sure that you have Mail set NOT to show you images. Mail Preferences->Viewing->Uncheck show remote content. That way, if you get emails from say, Land's End or something, you can choose whether or not to view the attached images, which of course consume bandwidth. (There will be a "load remote content" button on any email with that sort of content.
Install Click to Flash. That way no Flash content will play unless you click on it.
And if you really want to cut down on bandwidth, you can turn off images in most browsers. In Safari, if you enable the Develop menu, you can turn them off there. Open Safari and go to Preferences, then click on the Advanced tab. There's a checkbox at the bottom titled "Show Develop menu in menu bar". Check that then close the Preferences window.
You'll notice that in your menu bar between Bookmarks and Window you have a menu called Develop. Near the bottom of that menu list is Disable Images — click it. Now your browsing experience is image free. A bit drastic, but will cut down on bandwidth.
And of course - stay away from YouTube.
