First off, I suggest following Liz Ryan on LinkedIn.
Next, what you are being asked to do is beyond the scope of level 1 support. Level 1 support for the most part answer phones, open tickets, perform basic trouble shooting, unlock accounts, and perform password resets. Level 1 support follow scripts and knowledge base articles. Does that help you, not at all.
It is time to ask some questions.
Do you know why the engineer left, the real reason and not the company line? Are they going to be replacing the engineer that left?
Do you want to stay at this company with your current boss? If you don't, or you're not sure, you should start looking for a new position now. I don't see this getting better.
While the suggest made by to document everything you do is good, I sincerely doubt that your boss is going to recognize you as a contributor, from what you've mentioned so far you are most likely going to be rewarded with more work. Documentation makes doing your job easier. You don't have to remember how to do X, all you need to do is know where the documentation for how to do X is located. This is especially helpful for things that aren't done often, but are performed regularly.
Additionally someone who cannot be replaced cannot be promoted either. What you want to do it provide a level of service that makes people want to deal with you when they have a need or a problem. Share information, do not horde it.