You need to find every chest in the game. The Golden ones contain several special upgrade items (better health, permanent armor, etc. - see list below) which are counted for the Trophy Hunter achievement. Once you've collected all the Golden Chests and their content, the Trophy Hunter achievement is completed.
List of Golden Chest items :
Life container (life reserve is increased by 20%)
Professor's armor
Military armor (the resulting damage you take will be 40% less)
Great belt (allows you to carry more than two weapons)
Hit pill (accuracy is increased by 10%)
Roomy backpack (allows you to carry another weapon)
Helmets (reduces max damage by 10% each)
. (Source: http://zombotron.wikia.com/wiki/Chests)
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Several games on Armor Games have the wiki link located underneath the game, above the game comments section. A lot of information about the game can be found in these wiki articles...
@MrDayCee so i need to replay the whole game again because you can't check what you have and these place where the golden chest are, are random ? right ?
It's been a while since I've played this, but I don't think the golden chest placements are random -- my memory places them in the same spot for each run-through.