I don't agree with Nebten,
From
SRD,
Quote:
RESISTANCE TO ENERGY
A creature with resistance to energy has the ability (usually extraordinary) to ignore some damage of a certain type each round, but it does not have total immunity.
Each resistance ability is defined by what energy type it resists and how many points of damage are resisted. It doesn’t matter whether the damage has a mundane or magical source.
When resistance completely negates the damage from an energy attack, the attack does not disrupt a spell. This resistance does not stack with the resistance that a spell might provide.
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This is the default rule and it does not say that resistance to energy protects one's gear.. So unless otherwise noted, Resistance to Energy does not protect one's gear. Some spell or ability may say that the resistance gained from it also protects one's gear.
In case of spells, they will often allow you to save (in that case attended magic items are damaged only when a character rolls natural 1 on the save) or targets creature (PC) only. So magic items are rarely damaged during combat.
So, yeah, if a someone with fire resistance 10 sleeps in a fire, he will end up naked and covered with ash.
But, magic items made of wood or metal tend to have enough hardness to resist non-magical fire. Fire damage is halved before applying object's hardness.