Question: I'm going to the Elemental Plane of Fire, and I don't want my ice cream to melt. What's the least expensive and most portable method to keep my ice cream consistently intact?

Answer: 
Use the most powerful spell in the history of Pathfinder!

[**Prestidigitation!**](http://paizo.com/pathfinderRPG/prd/coreRulebook/spells/prestidigitation.html)

That spell allows you to chill 1 pound of non-living material.

If your GM allows it, using the custom magic item rules, you could make a box which would be permanently affected by the prestidigitation spell for as much as 1000 GP!

Prestidigitation would then be a permanent effect chilling the inner part of the "fridge" allowing it to chill all of the box's contents!
A box of sawdust.

"the ice was covered with sawdust. Ice was delivered to as far away as India"

<https://insulation.org/io/articles/a-history-of-refrigeration/>

<https://en.wikipedia.org/wiki/Ice_house_(building)>