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!
Seal some [Brown Mold](http://www.d20pfsrd.com/gamemastering/traps-hazards-and-special-terrains/hazards/special-hazards/brown-mold-cr-2/) in a container and put that container inside a larger, insulated container for your ice cream. The cost is the cost of the containers plus the cost of the brown mold (free if you can find it and harvest it).

That's a trick I've been using since 2ndE (the walk in freezers had a ring of warmth on a hook outside it). In this case, the freezer was double walled with the mold sandwiched between. When a friend wanted their own freezer, I had him build a similar room, took some mold from mine, put it in between the walls of his and launched a couple of fireballs into it. It was chilly in no time.