As with any graphic design project I really think it all starts with an idea or a problem that you want to solve. When I was going through school I remember making packing designs out of thin air to meet requirements, but the result was always incomplete-- no matter how visually striking you can make something, if it doesn't serve a purpose or solve a goal it's the equivalent of window dressing.
So first and foremost I think you should have an idea for packaging or possibly even reach out to someone who could use a packaging design (restaurants, small businesses, etc). Its only through having a concept can you narrow down your focus.
Only then can you really dig into the details.
There are a lot of free resources out there as well as some not free, but very verbose and detailed books about packaging design. One site I really enjoy visiting is Smashing Magazine's packaging design articles -- they often showcase some great packaging that you could use to get your metaphorical engines revving.
As for templates, in most cases I think it would be difficult to go without them, it really depends on what it is you are designing for though.
As a final personal aside, when I was in school I reached out to a local high scale restaurant to see if I could assist them as a graphic designer in anyway and I explained to them that I was trying to improve my portfolio. It just so happened that they were bottling their own wine and wanted to figure out what type of packaging their target demographic would respond to. After doing my due diligence and research I designed something that became one of the highlight pieces in my portfolio at the time, but it starts with reaching out!