Put update.ps1, install.ps1, record.ps1, and packages.config inside a git repository to enable tracking which versions you have installed at any one time. This means you can sync between systems and backup via any git host.
Update procedure is:
git pull ./update.ps1 git commit -m "Updated $env:computername" git push
Install procedure is:
git pull # edit packages.config to add <package name="mypackage" /> ./install.ps1 git commit -m "Installed mypackage" git push
It can be very nice to know exactly which versions were installed at some point in history just in case there's an issue with a new version. But it can be trouble to maintain it, so don't worry too much about merging when syncing between different systems; just let it overwrite, then commit with the computer name you updated and push. When you search through your git history you can see which versions were installed on each computer at points in time. (It might be a little messy, but it's fine for a fallback.)
See comments in install.ps1, update.ps1, and record.ps1 for details about what they do.