Besides being Minn-stf archivist, I also have a personal collection of fannish materials dating mostly 1997–present. It mostly consists of official publications of cons I've attended and flyers picked up thereat. It therefore has a strongly upper-midwest bias, but if flyers were sent in from afar, or appeared at a Worldcon, I have those too. Since I am primarily a con-fan, there is also a bias towards con materials over over stuff that may have been available (fanzines, book clubs, self-pub adverts…).
Crucially, my collection is organized by year and easily accessible in a filing cabinet. (i.e. It isn't all in a heap in a cardboard box in the basement.) As of 2017, the size is just over one linear cubit and is growing at a pretty consistent 3 fingers per year. When I die, the job of the librarians that have to sort through my stuff shouldn't be too painful.
If you want to know something about a con in the upper midwest and can't find it at the con's current website, fanac.org, or other attempts to catalog all of fannish knowledge, there is a chance I can answer the question. I can also provide scans of smaller items. In some cases, I can send you a copy for keeps if I have multiples.
Write to matthew dot strait at this domain name.