That's not much of a brief. I wouldn't take the job without a little more direction or at least without some discussion leading to something more concrete than "heroic and important". Do they want just the packages, without props? Reflections? How about backgrounds? It's not that I need to be told what to do, but that I need to know what the client wants, or at least that they're okay with what I suggest if they don't know. Otherwise you're in the "client from Hell" situation, and that almost never ends well.

There's not much you can do with just the face of a container (and you do need to be pretty much face-on for branding) but I'd be inclined to use a much shorter lens and get as close to even with the bottom of the package as possible. Exactly what length depends on the format you're shooting and the package size, but it is going to have to look somewhat keystoned in order to look heroic in two dimensions. 24mm full-frame equivalent likely wouldn't be too far out, although a 28-35mm full-frame equivalent may work as well if the lens is internal focus, can focus closely enough, and gets short enough at the required distance. (With props you can use near-far relationships and keep the package square, even if that means squaring it in post.) A 100mm lens gives you little choice but to shoot flat and straight on, since if you shoot at an angle, the resulting package geometry will make it look, well, distant and small even if it fills the frame.

A glossy or semi-gloss surface that will provide a reflection would also be a probable choice. Exactly what that surface might be depends on the product and the packaging—it might be a bit of plexi or laminate, varnished wood or polished stone. Whatever works with the colours and the product. For all I know right now, a float may work.

You can manage the glossiness with lighting angles; there should be no need to use a polarizer. Unless, that is, you are provided with less-than-perfect packages having sloppy rounded corners. If that's the case, then you're in for a horribly long time in post anyway, so it might not be worthwhile trying to balance lighting and colour across a wide-angle frame with a polarizer anyway.

I'd be inclined to use a gradient background for a straight pack shot, but that really depends on the product. Without knowing what it looks like, I can't give you any advice other than to work with figure/ground contrast. The product has to stand out.

Again, if I had my druthers, I'd chase a better brief first and try to get a sketch approved before going any further. Without something to work towards, you turn the job into a game of Battleship, hoping that you hit a hidden target.