RE Upgrading to Sierra (assuming that at some point that would be useful ~ desirable ~ necessary)

It is still the case that I have zero access to high-speed qua broadband Internet access in order to acquire/install the latest bits and pieces. I would ostensibly require the OS cum installer to be on a USB drive or similar — which apparently doesn't exist.

Other than my being forced into upgrading my hardware to acquire the latest MacOS, I don't see other options. Any suggestions?

I can update most of my 'essential' apps by downloading same separately online via other methods. But I don't relish losing Office for the Mac 2011 and other such entities simply because I upgrade to an incompatible OS. Again, any suggestions?