“Yardsale!” is more than just another short documentary about a quirky topic set in the ever-quirky state of New Jersey. The genial Robert A. Emmons Jr., a filmmaker and pop-culture enthusiast, provides an informal yet informed look at a bit of cultural history. Using footage of rummage sales and other nooks of suburban life, he explores the phenomenon of curbside consumption, still very alive in the EBay age. The film includes Saturday morning treks and commentaries that pop in without any intrusion. More than just a snapshot of offbeat folk (though these types are given their due) and the old adage that things reinvent us, this little study captures an infectious love of Americana. An occasional gimmick may show up (is there some unwritten contract between indie musicians and their cinematic counterparts?), but the structure is so well oiled that you will want to take Emmons’ knowledge home with you.