There is a last Combo update download that makes Snow Leopard 10.6 complete.
You should get that and also check for more updates from Apple servers by use of
the Software Update selector in menu beneath the Apple icon in Finder.
The Combo Update 10.6.8 v1.1 is available for download (works to finish
the Snow Leopard full installation) from this Apple support page link:
• Mac OS X 10.6.8 Update Combo v1.1
For continued offline use, you could get an externally enclosed hard disk drive, then
get a free (demo) of SuperDuper cloning utility, to make a copy that may save you
the effort of re-downloading the entire OS X + Combo update. If you learn how to
make and use Clones, that can save you. An external drive should be self-powered
and not rely on USB port power, if its Clone is ever called upon to start up the Mac.
This may be important should the internal MacBook hard drive fail. You would be
able to replace the internal hard drive, then use the running clone on external drive
(with its copy of Clone utility in place) to ready a replacement HDD, then clone the
content of the external drive into a newly installed internal hard drive.
A helpful product to have, if one wants to prepare a replacement hard drive for a
new OS X installation, without installing the drive first, is a wire kit; the OWC also
has replacement drives, among other upgrade parts & instruction video:
newertech universal drive adapter USB... kit (includes power adapter)
https://eshop.macsales.com/item/NewerTech/U3NVSPATA/
For examples of upgrade parts, and a way to find ones most likely compatible
with your computer, there is a page at OWC that may be helpful.
https://eshop.macsales.com/upgrades/
In the eventuality of replacement of the internal drive, usually they can be expected
to fail after a few years. In the process of acquiring the correct spec replacement,
you could get an external USB wire kit that allows you to prepare a new HDD to
accept an installation of OS X before the hard drive is installed. You could do that
ahead of time, with the correct system (fresh install/clone to new hard drive) while
the computer is still running correctly. Once the HDD fails, it won't work.
Main portal to portable Apple repair guides:
https://www.ifixit.com/Device/Mac_Laptop
{Note your build model identifier or processor speed may be used to identify
the unit among others in these guides; if your unit is a MacBook Pro instead
of MacBook, select the correct guide section from main page}
Your model is likely among those this Guide covers:
https://www.ifixit.com/Device/MacBook_Core_2_Duo
• MacBook Repair guides - iFixit:
https://www.ifixit.com/Device/MacBook
There are good instructions on the iFixit repair guide pages so the task can be
done if you have a second means of seeing them online. Or if you were to save
the web page instead of printing as PDF for offline reference, that would likely
keep any links to other places (in the original page) alive & accessible.
In any event...
Good luck & happy computing!