I’d love to add this pack to my Libre Game Assets collection but, currently, it’s in a legal gray zone.
Specifically, “Creative Commons”, “CC-BY” and so on are trademarks and you’re only licensed to use them if you don’t hang additional restrictions off the license, which your “DON’T RE-SELL THIS PACK!” counts as if it carries the weight of law rather than just being a very emphatic “Please don’t do this”.
Here’s the relevant part of their trademark policy:
If you place any restriction on use of a CC-licensed work that has the effect of limiting or further conditioning the permissions granted to the public under the standard CC license, you must not use any CC trademarks or branding in connection with the license or in any way that suggests the work is available under a CC license.
In fact, given the way the law works, if they chose to sue you, they’d probably win based on the “How would a reasonable everyman interpret this?” test seeing it as a legal requirement.
Basically, trademark law cares a lot about protecting the value of a brand, and hanging additional restrictions off a CC license adds uncertainty, which makes the CC name and badges less valuable as a signal to non-lawyers.
It’s the same reason ads say “better than the next leading brand” instead of naming that competitor. Trademark law doesn’t allow them to piggy-back off their competitor’s brand recognition without permission.
…plus, your restriction would only apply to the person who downloads it directly from you. Because the CC-BY governs them giving copies to other people, only the CC-BY would apply to other people they gave it to. (Basically, CC licenses work because they do an imaginary copy-paste of the rules/permissions every time someone makes a copy… and they only copy-paste the ones inside the CC-BY.)
That said, you can make it unattractive to resell by taking advantage of this clause of the license…
identification of the creator(s) of the Licensed Material and any others designated to receive attribution, in any reasonable manner requested by the Licensor
…to require a byline that explicitly says it can be downloaded for free at the given URL.
(That would more or less leave resale to cases where people are adding value, such as selling DVD-R compilations in parts of the world with flaky Internet or selling the service of having filtered through all the free stuff to find the best stuff matching a certain theme.)