I never knew that gifted kids are more likely to have some sort of collection. DS's current collection is twisty puzzles, but over the years, he has had other passions.
But I wonder -- is that connected at all with pack-rat-ism? All three of us in this household are horrible pack-rats. "Well, this will be useful someday" or "I'd want it as soon as I get rid of it" and so forth. In fact, ds has always collected odds and ends of trash from outside (amazing how many nuts and bolts and such can be found!), because "I could make something from that." One summer, every cardboard box or tube was snatched up by ds so he could make something with it. (Three foot high, 10x20 room filled with games he made that summer....)
But surely there are some who escape unscathed, no? ;-)