The present invention includes a shopping cart frame with mounting bracket units connecting caster wheels and having a plate secured underneath the base with a caster pin receiving hole and spaced-apart flanges flanking the hole and abutting on the base; a shopping cart with a support bar between side uprights for forwardly propping up a primary basket and rearwardly hanging a secondary basket; a cart with a plastic basket having rear structural tubes sheathing the frame's side uprights and being secured thereto; a modular method of making different cart models by providing multiple sets of components with cooperating mounting surfaces for interconnection; a modular plastic basket with a hooked-on suspended tray and a channel-shaped overlay detachably snapped over the edge and tray; a one-piece molded plastic basket with independent branching tubular sections with different thicknesses; and an independent gas-assisted injection method for molding a one-piece plastic basket.