An old topic, but I'll weigh in from experience. Like others have stated, it is based on your insurance company. I had a minor flood in my basement due to a leaky pipe. My insurance covers replacement value of items. One item that was damaged was the Ep. 1 Royal Starship that was unopened. Since this wasn't an item that was currently available, I showed the insurance company my purchase price and what the going rate was on ebay. They gave me the ebay price.
A couple years ago, I had a house fire. Most of my collection had been moved out by then, but I did have a few items in house. Since the damage was mostly from smoke, most of my stuff was restored (I believe they put stuff in a chamber with ozone). It worked surprisingly well, considering what I had in the house was mostly books, boxed legos and some carded figures. You would never know they were exposed to smoke. Since this was a large loss in terms of items (which included all my other possessions), I received a bulk check for everything. My insurance provides replacement in kind cost. For example, I had a 60" TV that was damaged and could not be repaired. Even though it was close to ten years old (an HD projection TV), I was able to replace it with a modern TV. What the insurance does is have you find a new 60" TV and give them the value for it. They then depreciate the value based on the age of the old TV to come up with value. You get the depreciated value, but then you get the depreciation back once you buy the item and replace the old item. One thing they don't tell is that you can use depreciation of one item and other items. For example, say you come up with a value of $50K for all your items (and yes, you have to do all the leg work and price everything with references to where you got the value) and everything gets depreciated at 50%, you get a check for $25K and can recover the other $25K when you make purchases. So if you have a TV that is valued at $4K and they give you $500, you can either buy a $4K TV to get the additional $3.5K, or you could buy a $5K TV and get $4.5K in depreciation back and that just comes out of the total $25K depreciation pot.
As for collectables, yes it is a good idea to take pictures and work out values, but most likely your possessions coverage is high enough to cover everything. Some companies do require an extra rider to cover stuff. It just depends on what your company covers.