An accessory attachment system comprising: a channel element (30, 160, 160A) comprising a rear wall (32, 162), a shelf (36, 166) extending forward relative to the rear wall (32, 162), and a lower lip (37, 167) extending generally downward from a leading edge of the shelf; and an accessory (52, 62, 62A, 63B, 72, 82, 92, 112, 112A) arranged to be repositioned relative to the channel element (30, 160, 160A), the accessory including an accessory body (60, 130) configured to be received by the channel element, wherein the accessory body comprises at least one restraint cooperating element (111, 138, 184) and a pivotally mounted spring-biased clasp including a hook element configured to engage the lower lip when the accessory body is received by the channel element; characterized in that: the channel element (30, 160, 160A) comprises a plurality of laterally spaced accessory motion restraints (174, 188) located above the shelf (36, 166); and the at least one restraint cooperating element (111, 138, 184) is configured to cooperate with one or more accessory motion restraints (174, 188) of the plurality of laterally spaced accessory motion restraints to inhibit lateral movement and rotation of the accessory body (60, 130) relative to the channel element (30, 160, 160A) when the accessory body (60, 130) is received by the channel element (30, 160, 160A); wherein the accessory attachment system comprises one of the following features (a) or (b): (a) the plurality of laterally spaced accessory motion restraints (174, 188) comprises a plurality of apertures or recesses defined in the channel element (30, 160), and the at least one restraint cooperating element (111, 138, 184) comprises a plurality of protrusions (111, 138) extending from a surface of the accessory body (60, 130) and arranged to be received by multiple apertures or recesses (174, 188) of the plurality of apertures or recesses; or (b) the plurality of laterally spaced accessory motion restraints (174, 188) comprises a plurality of protrusions extending from a surface of the channel element, and the at least one restraint cooperating element (111, 138, 184) comprises multiple laterally spaced apertures or recesses defined in the accessory body and arranged to receive multiple protrusions of the plurality of protrusions. a channel element (30, 160, 160A) comprising a rear wall (32, 162), a shelf (36, 166) extending forward relative to the rear wall (32, 162), and a lower lip (37, 167) extending generally downward from a leading edge of the shelf; and an accessory (52, 62, 62A, 63B, 72, 82, 92, 112, 112A) arranged to be repositioned relative to the channel element (30, 160, 160A), the accessory including an accessory body (60, 130) configured to be received by the channel element, wherein the accessory body comprises at least one restraint cooperating element (111, 138, 184) and a pivotally mounted spring-biased clasp including a hook element configured to engage the lower lip when the accessory body is received by the channel element; the channel element (30, 160, 160A) comprises a plurality of laterally spaced accessory motion restraints (174, 188) located above the shelf (36, 166); and the at least one restraint cooperating element (111, 138, 184) is configured to cooperate with one or more accessory motion restraints (174, 188) of the plurality of laterally spaced accessory motion restraints to inhibit lateral movement and rotation of the accessory body (60, 130) relative to the channel element (30, 160, 160A) when the accessory body (60, 130) is received by the channel element (30, 160, 160A); wherein the accessory attachment system comprises one of the following features (a) or (b): (a) the plurality of laterally spaced accessory motion restraints (174, 188) comprises a plurality of apertures or recesses defined in the channel element (30, 160), and the at least one restraint cooperating element (111, 138, 184) comprises a plurality of protrusions (111, 138) extending from a surface of the accessory body (60, 130) and arranged to be received by multiple apertures or recesses (174, 188) of the plurality of apertures or recesses; or (b) the plurality of laterally spaced accessory motion restraints (174, 188) comprises a plurality of protrusions extending from a surface of the channel element, and the at least one restraint cooperating element (111, 138, 184) comprises multiple laterally spaced apertures or recesses defined in the accessory body and arranged to receive multiple protrusions of the plurality of protrusions. (a) the plurality of laterally spaced accessory motion restraints (174, 188) comprises a plurality of apertures or recesses defined in the channel element (30, 160), and the at least one restraint cooperating element (111, 138, 184) comprises a plurality of protrusions (111, 138) extending from a surface of the accessory body (60, 130) and arranged to be received by multiple apertures or recesses (174, 188) of the plurality of apertures or recesses; or (b) the plurality of laterally spaced accessory motion restraints (174, 188) comprises a plurality of protrusions extending from a surface of the channel element, and the at least one restraint cooperating element (111, 138, 184) comprises multiple laterally spaced apertures or recesses defined in the accessory body and arranged to receive multiple protrusions of the plurality of protrusions.