On my Mint, I set the software cache to keep all the package downloaded. I make back-up of the package using aptonCD (or DVD) every time I make big update (like office update). This method was very useful, especially when I have to install update on other offline pc. Just sudo dpkg -i *.deb on the extracted ISO image and my others pc (the offline ones) also get the update.
ASUS 1215B AMD E-350 with LMDE KDE, LMDE MATE, Precise Puppy, and Saluki