While you can't check your post office box, just about anything else you can do at your local post office can be done via the Postal Service's automated phone system, by calling 1-800-ASK-USPS (1-800-275-8777).
Whether it's getting ZIP Code information to mail Grandma her birthday card, checking mailing rates for that package to Canada, or tracking Priority Mail or Express Mail shipments, you can do it all here. In addition, you can find out where the nearest Post Office is, enter a change of address order, or even buy stamps.
While the automated system is available 24/7, they also have live operators to help you find out what's what Monday through Saturday starting at 8:00 am Eastern Time for the more complicated stuff.
It's all the fun of a trip to the Post Office, but without having to wonder about that creepy guy standing over in the corner.