I work with Rindr. Personally, my offerings through her tend to not be physical ones. And this is something you'll find throughout most of the frost jotnar: they do not appreciate physical offerings (foods, drinks) as much as they appreciate actual labor, work and effort on your part. They are very stoic, and therefore also hard to please. I've found that taking direct action is the best way to offer things to them.
For instance, because of Rindr's experiences with sexual assault- I've donated to a local woman's shelter where I live and this seemed to work.
The site suggests if you're looking for some kind of physical offering, you could freeze flowers or berries and other things normally not associated with winter in ice (easily done in a freezer, with limited space).