You need to ask your Agent. (let them know you are not talking about a few hundred dollars either, because insurance guys will just think of them like cards, books, etc and not think really about it)Covered by renters insurance, most likely is the answer but if they are stolen off premesis you won't get enough coverage as you probably only get 10% for property off premesis.
Covered by home insurance, depends. Some companies out there have gotten wise and have a limitation on the max of any one particular card as well as a max on trading cards. Not all companies cover them to your contents amount at least not in Texas(1000 max total). This is something companies changed back in 2008
I will point out that you gotta use a coverage off of a policy. They can't just mysteriously desappear. Roof leaks, better hope wind knocked off the roof or shingles because wind driven rain is not covered..
Say someone just takes your bookbag, probably not covered as companies look for some sign of forced entry. Car is stolen your auto insurance isn't going to pay you a dime for the cards. Cards that are just "walk away" are not going to be covered.
Most common type of loss you could have is fire, hot water heater bursts and well theft, but how many people break into a house or apartment just to take Magic cards. Sure someone could break into your car at an event but if you are bringing expensive stuff you won't have enough coverage or cheap stuff and you won't get passed your deductible.
You may ask why would renters cover more then home policies well the simple answer is the policies for homes are updated ever year or two. Renters policies filed with the each state typically are updated ever 10 years so they are behind with the times.
As for documentation you better have it for any of the big guns. Video or pics.
This is how it works in Texas and well Texas is unique to country in coverages. If you live in California, New York, New Jersey or Florida, well they tend to have differnt rules then the rest of the country as well.
[Edited 5 times, lastly by slurpee on October 26, 2010]