grädde is made out of milk (in principle: there are a few things that are called grädde by analogy, in compound nouns e.g. kokosgrädde 'coconut cream')
kräm refers to consistency (as in 'creamy') – it can be 'cream' or 'paste' in English
Thus, vispgrädde is 'whipped cream'
but tandkräm 'toothpaste', hudkräm 'skin cream' and chokladkräm is 'chocolate cream'
I don't think that's correct, actually. A gräddkanna is a creamer in the sense of a pitcher. But since you were going grocery shopping, I'm assuming you meant a small package with a non-dairy creaming agent that you pour into coffee. We don't really have a common word for that in Swedish, but you could mjölkpulver if it's in powder form.
Apologies if my assumption is incorrect, but I'm guessing this is not what you were going shopping for :)
There's also kaffegrädde, quite literally "coffee cream", which is what you use for the more general sense of creamer. It's typically dairy-based, though - half/half, or similar.