|Egg shipping box (source)|
The site of the Smithsonian Postal Museum (Washington, USA) offers a lot of interesting contents for mail lovers. Even for those who are not able to visit the Museum, we can still enjoy its virtual exhibitions.
If you have some spare time and like postal history, I recommend you Welcome to the Railway Mail Service (by Miriam Pysno & Katherine Fetter) and 100 Years of Parcels, Packages, and Packets, Oh My! (by Nancy A. Pope).