What does the percentage value on my gear represent?

Solution 1:

It is a sort of combination durability/quality statistic. Higher values improve the quality of the equipment. For example, more damage from weapons, better protection from armour.

It is also a measure of durability. Sometimes when you are hit your armour will be damaged. This decreases that number, and the associated benefit. I have yet to encounter a situation that will damage weapons (The jesters don't count), though I have only played through a single time. The character named Ubuntu gives the option to repair equipment. He can only repair it up to 100% though. I have used this to improve weapons, armour, and rings that were damaged when found, as well as armour that was damaged in combat.

Solution 2:

It appears to be a percentage of maximum damage your character can do with that item. According to the Unepic Wiki, the light spear does 28 damage. Yours does 32 damage. While, technically, that would be 114%, it seems to fit the pattern.

The wiki does not list the other two weapons. So, I'm going to assume that it is incomplete or perhaps incorrect with regard to the maximum damage numbers.

But, not having played the game extensively, that's the impression I got.