So much great advice already. It really all depends on where you are located as to how much per yard you can get. In my area (upstate NY) $4 per yard would be a fair price for an estate sale and if word got out to many quilters chances are you will be able to sell a lot. If this is good quilt shop quality fabrics that includes newer designs you should have no trouble asking and getting $4 per yard with no cutting down (buyers must take as is), but you always get people who think it should be less. If the fabric is older calicos like JoAnn fabrics "keepsake Calico" lines you won't get more than $2 per yard, same for most walmart fabrics (VIP is the most common manufacturer) and believe me most quilters can spot the difference immediately even without seeing the selvage. Solids sell for less. But if you have a lot of name brand fabrics (check the selvage edge of her fabrics) like Moda, Hoffman of California, Robert Kaufman, Kona Bay, Timeless Treasures (these are just the few name brands I could think of off the top of my head) or Batiks you should have no problems asking $4 per yard and getting it. Garage sale you may be able to sell at $4 per yard, but most people who go to garage sales expect to pay much less (around $2 or $3 per yard for name brand, less for no name brand or older fabrics). If your mom had vintage stuff like feed sack you can command more for it. But it is very hard to tell feedsack unless it is still in feedsack form. Some can tell by the weave. You could try putting an ad on Craigs list for the entire lot. But you will need to have lots of pics and a good idea of how much yardage there is. If she has a room full of stash, you could try asking a set figure for the whole lot and not bother with measuring how much fabric there is. What to ask is hard to say without having any idea at all of what you have.
Magazines you probably won't find anyone willing to pay more than .25 per issue and that is assuming the magazines are complete and no patterns or pages are missing. You might be better off bundling the magazine in bundles of 10 and price it for $2 per bundle or pricing 1 for .25 10 for $2.
Books you may be able to get around $4 or $5 each. Key words quilters look for in ads are "fabric" or "quilting cotton". I am thinking your mom may have also had a lot of tools, like rulers, cutting mats, rotary cutters and blades. If so advertise "quilting supplies including rulers and cutters (if she had them)". If you hold a sale, I would recommend selling yardage as is. It would be a lot of work for you to cut down pieces and you could end up with a lot of small leftover bits that won't sell. You will need to measure all pieces and put tags on them for the amount of yardage.
Bundle up kits, precuts and fat quarters separately. A good rule of thumb is half price what the original item cost. So if kits, patterns, precuts etc still have a price tag on them offer them at half off the tag price.