Due the used grammar zero value.Im really sorry to say this.However, the "s" end the end kills this domain name.Btw: The plural of "Rucksack" is "Rucksäcke".
Yea I know that it is wrong in German, you are right. "Rucksacks" seems to be widely used in the UK and has global 14,800 exact searches. For example this from insights "Caution, heavy load: Children are damaging their backs with excessively full school rucksacks"
The only time I have ever heard the term "RuckSacks" used was in reference to the military. It's an everyday used term in the military, but outside of that it's not common.
Kids refer to their school bags as "back packs" or "book bags".
As for value, Im thinking $x to very low $xx.
The singular version fits the extension much better.