Dialect thing. People should get what you mean though. In general I think the distinction is that a "rucksack" is more likely to be a small, old fashoned, leather or canvas thing made for carrying hiking gear, whereas a "backpack" is what a student probably uses, unless they use a "bookbag" which is sometimes a backpack, but can also be a bag of pretty much any sort fit for carrying books.
Sure, it definitely has an old-timey ring to it though. My (native-born American) grandfather used it quite a bit.
It has a connotation of a backpack used for storage or hiking, and it is still frequently used in the military. A frequent event in bootcamp is a "ruck march" where soldiers hike for many miles with a complete "kit" -- a full "rucksack".
For comparison, I would never call a student's bookbag a rucksack.
Здесь and тут are virtually interchangeable outside set expressions ("тут" is considered more colloquial). They both mean "here" literally. "This place", I mean.
- AFAIK, they are always interchangeable in our course. I think we did not use any set expressions (except, maybe "тут и там") that require тут
- тут же is a very useful expression that means "straight away"
Вот is connected to the idea of pointing at the thing, showing it to a listener ("here is it, look"). Maybe even literally.
Has anyone seen the movie "Trading Places"?
In it, in one scene, Jamie Lee Curtis pretends to be a German tourist, all done up in long braids and lederhosen, and she refers several times to her "rooksack" (rucksack).
That's the first time I ever heard the term. But then, I've never been back-packing in Europe.